Device transferring method, and device arraying method and image display unit fabricating method using the same

ABSTRACT

A method of selectively transferring devices arrayed on a first substrate to a second substrate on which an adhesive resin layer is previously formed is provided. The method includes steps of selectively heating the adhesive resin layer on the second substrate by laser irradiation from the back surface side of the second substrate, and curing the selectively heated portions of the adhesive resin layer, thereby adhesively bonding those to be transferred of the devices to the second substrate. At this time, portions, corresponding to the devices, of the adhesive layer are heated directly or indirectly via the devices or wiring portions by laser irradiation from the back surface side of the substrate. The heated portions of the adhesive resin layer selectively exhibit the adhesive forces. The heated portions of the adhesive layer are then cured, so that only the devices to be transferred are selectively transferred to the second substrate. As a result, only the devices to be transferred can be done so with certainty, efficiency, and accuracy without exerting adverse effect on other parts.

RELATED APPLICATION DATA

The present application claims priority to Japanese Patent ApplicationNos. P2001-112401 filed on Apr. 11, 2001; P2001-169857 filed on Jun. 5,2001; P2001-194890 filed on Jun. 27, 2001; herein incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a device transferring method oftransferring devices such as semiconductor light emitting devices, and adevice arraying method and an image display unit fabricating method fortransferring finely formed devices to a wider region by using the devicetransferring method.

At present, an array of a number of fine devices, electronic parts,electronic devices, or electronic parts formed by burying the abovedevices or parts in an insulator such as a plastic material are beingextensively used for electronic equipment.

The assembly of an image display unit by arraying light emitting devicesin a matrix is performed in two manners. For a liquid crystal display(LCD) or a plasma display panel (PDP), the light emitting devices aredirectly formed on a substrate, and for a light emitting diode display(LED display), single LED packages are arrayed on a substrate. Inparticular, for an image display unit such as an LCD or PDP, deviceisolation cannot be performed, so that in general, at the beginning ofthe fabrication process, devices are formed in such a manner as to bespaced from each other with a pitch equivalent to a pixel pitch of theimage display unit.

For an image display unit such as an LCD or PDP, device isolation cannotbe performed, so that in general, at the beginning of the fabricationprocess, devices are formed in such a manner as to be spaced from eachother with a pitch equivalent to a pixel pitch of the image displayunit.

On the other hand, for an image display unit such as an LED display, LEDchips are packaged by taking out LED chips after dicing, andindividually connecting the LED chips to external electrodes bywire-bonding or bump-connection using flip-chip. In this case, before orafter packaging, the LED chips are arrayed with a pixel pitch of theimage display unit; however, such a pixel pitch is independent from anarray pitch of the devices at the time of formation of the devices.

Since an LED (Light Emitting. Diode) representative of a light emittingdevice is expensive, an image display unit using such LEDs can befabricated at a low cost by producing a large number of LEDs from onewafer. To be more specific, the cost of an image display unit can belowered by reducing the size of an LED chip from about 300 μm square(ordinary size) to several tens μm square, and producing an imagedisplay unit by connecting such small-sized LED chips to each other.

From this viewpoint, there have been known various techniques oftransferring devices densely formed on a substrate to a wide region insuch a manner that the devices are enlargedly spaced from each other inthe wide region, thereby obtaining a relatively large display unit suchas an image display unit. For example, U.S. Pat. No. 5,438,241 hasdisclosed a thin film transfer method, and Japanese Patent Laid-open No.Hei 11-42878 has disclosed a method of forming a transistor array panelfor display.

In the transfer method disclosed in U.S. Pat. No. 5,438,241, devicesdensely formed on a substrate are coarsely re-arrayed by transferringthe devices densely formed on the substrate to an extensible substrateprovided with an adhesive layer, extending the extensible substrate inthe X direction and the Y direction while monitoring a device arraypitch and positions of respective devices, and transferring the deviceson the extended substrate onto a desired display panel. In the techniquedisclosed in Japanese Patent Laid-open No. Hei 11-142878, thin filmtransistors forming a liquid crystal display portion on a firstsubstrate are all transferred onto a second substrate, and the thin filmtransistors are selectively transferred from the second substrate to athird substrate in such a manner that the transferred transistors arespaced from each other on the third substrate with a pitch correspondingto a pixel pitch.

In the case of producing image display units by the above-describedtransfer techniques, it is required to selectively, certainly transferonly devices to be transferred, and to efficiently, accurately transferonly devices to be transferred. In general, there has been known amethod of using a thermoplastic resin as an adhesive for mounting,microelectronic parts, electronic devices, or electronic parts formed byburying these electronic parts or electronic devices in an insulatorsuch as a plastic material, on a mounting substrate. For example,necessary portions of a mounting substrate are coated with athermoplastic resin, and electronic parts are placed on the portions ofthe mounting substrate; and then the entire substrate is heated, tosoften the adhesive and cool it, thereby fixing the electronic parts onthe substrate. Alternatively, the entire surface of the substrate iscoated with a thermoplastic resin, and electronic parts are placedthereon; and then the entire substrate is heated, to soften the adhesiveand cool it, thereby fixing the electronic parts on the substrate. Inaddition, there has been known a method of obtaining the same structureby removing the exposed adhesive by etching or plasma treatment.

In the case of using such a method, however, there arises a problem thatsince the electronic parts must be placed one by one, the work becomescomplicated, and since the entire substrate is heated, there occurs thepositional deviation and peeling of other parts. For example, in thecase of arranging all of parts on the supply side on a substrate withthe array pitch kept as it is, it is possible to use of transferring theparts on the supply side to the substrate. In the case of using athermoplastic resin for this transfer, the entire substrate is heated bya high frequency heating treatment or exposed to a heating atmosphere,to allow the thermoplastic resin to exhibit an adhesive force strongerthan an adhesive force of the parts against the supply side, therebytransferring the parts to the substrate side.

Parts to be transferred and parts not to be transferred can beselectively transferred by using the above transfer method; however,according to the existing technique, it is difficult to heat only thedesired parts, and therefore, this method has been not put intopractical use. In the case of the overall heating, if an excess portionis coated with a thermoplastic resin, the array positions of parts maybe possibly changed by the flow of the thermoplastic resin. Accordingly,in general, it is required to coat portions, at which parts are to beplaced, of the substrate with a resin, and therefore, it fails to solvethe above-described problem associated with the complicated work.Similarly, there may be considered a method of picking up electronicparts once from a supply source by using an attracting head and placingthem on a substrate; however, in this method, if the entire substrate isheated in the case of fixedly transferring the electronic parts from theattracting head to the substrate, there may occur an inconvenience thatother parts having been already fixed to the substrate be peeledtherefrom.

In the case of performing overall heating by laser irradiation, ifeither of a thermoplastic resin and each part has a low lightabsorptivity against laser beams, there occurs a problem that thethermoplastic resin is not heated to a desired temperature. Also, if theparts are taken as heating planes, the parts are required to have a highheat-resistance. Further, in the case of performing overall heating bylaser irradiation, it is required to select such a wavelength of laserbeams that at least one of a thermoplastic resin, each part, and wiringon the substrate has a high light absorptivity against the laser beams.

For example, there has been known a device transferring method shown inFIGS. 1(a) and 1(b), wherein devices 103 are arrayed on an adhesivelayer 102 on a base substrate 101 as shown in FIG. 1(a), and are pickedup by using an attracting head 104 as shown in FIG. 1(b), to betransferred to an adhesive layer 106 on another substrate 105.

This method, however, has problems that since a plurality of steps ofpicking up each device by the attracting head, moving the attractinghead, and placing the device to the substrate are required to transferthe devices, the transfer process becomes complicated, and since aplurality of kinds of equipment are required to be provided, the cost israised, and that since the devices must be picked up one by one formounting the devices, the mounting work becomes very complicated, and ittakes much time to transfer the devices. If it is intended to improvethe working efficiency of the mounting machine for shortening the timerequired to mount the devices, there occurs another problem that theaccuracy of arraying of the device at the time of mounting the devicesis degraded. Additionally, in the case of using the existing mountingmachine, the positioning accuracy at the time of arraying devices has alimitation to about 10 μm, and therefore, it is difficult to furtherenhance the positioning accuracy by the existing positioning method.

SUMMARY OF THE INVENTION

The present invention provides a device transferring method capable oftransferring with certainty only those devices to be transferred ofdevices on a substrate, thereby efficiently and accurately transferringthe devices, and provides a device arraying method and an image displayunit fabricating method using the device transferring method.

According to an embodiment of the present invention, there is provided adevice transferring method of selectively transferring devices arrayedon a first substrate to a second substrate on which an adhesive resinlayer is previously formed, the method including:

-   -   a heating step of selectively heating the adhesive resin layer        on the second substrate by laser irradiation from the back        surface side of the second substrate; and    -   a curing step of curing the selectively heated portions of the        adhesive resin layer, thereby adhesively bonding those to be        transferred of the devices to the second substrate.

With this device transferring method, portions, corresponding to devicesto be transferred, of the adhesive resin layer are heated directly orindirectly via the devices or wiring by laser irradiation from the backsurface side of the substrate. The heated portions of the adhesive resinlayer are allowed to selectively exhibit adhesive forces. By curingthese portions of the adhesive resin layer, only the devices to betransferred can be selectively transferred to the second substratewithout peeling and positional deviation of other parts. In this case,it is not required to selectively form the adhesive resin layer bycoating.

According to the present invention, there is provided a device arrayingmethod of re-arraying a plurality of devices arrayed on a firstsubstrate to a second substrate, the method including:

-   -   a first transferring step of transferring the devices from the        first substrate to a temporarily holding member in such a manner        that the devices are spaced from each other with a pitch larger        than a pitch of the devices arrayed on the first substrate and        holding the devices on the temporarily holding member;    -   a covering step of covering the devices held on the temporarily        holding member with a resin;    -   a dicing step of dicing the resin so as to isolate the devices        from each other;    -   a second transferring step of transferring the resin-covered        devices held on the temporarily holding member to the second        substrate in such a manner that the resin-covered devices are        spaced from each other with a pitch larger than a pitch of the        resin-covered devices held on the temporarily holding member;    -   wherein the second transferring step includes the steps of        selectively heating an adhesive resin layer on the second        substrate by laser irradiation from the back surface side of the        second substrate, and curing the selectively heated portions of        the adhesive resin layer, thereby adhesively bonding those to be        transferred of the resin-covered devices to the second        substrate.

With this device arraying method, since the devices can be efficientlyand performed with certainty and accuracy, it is possible to smoothlyperform enlarged transfer by means of which the devices are transferredin such a manner as to be spaced from each other with an enlarged pitch.

According to an embodiment of the present invention, there is providedan image display unit fabricating method of fabricating an image displayunit including light emitting devices disposed in a matrix, the methodincluding:

-   -   a first transferring step of transferring the light emitting        devices from the first substrate to a temporarily holding member        in such a manner that the light emitting devices are spaced from        each other with a pitch larger than a pitch of the light        emitting devices arrayed on the first substrate and holding the        light emitting devices on the temporarily holding member;    -   a covering step of covering the light emitting devices held on        the temporarily holding member with a resin;    -   a dicing step of dicing the resin so as to isolate the light        emitting devices from each other;    -   a second transferring step of transferring the resin-covered        devices held on the temporarily holding member to the second        substrate in such a manner that the resin-covered devices are        spaced from each other with a pitch larger than a pitch of the        resin-covered devices held on the temporarily holding member;    -   herein the second transferring step includes the steps of        selectively heating an adhesive resin layer on the second        substrate by laser irradiation from the back surface side of the        second substrate, and curing the selectively heated portions of        the adhesive resin layer, thereby adhesively bonding those to be        transferred of the resin-covered devices to the second        substrate.

With this image display unit fabricating method, the light emittingdevices are arrayed in a matrix by making use of the above-describeddevice transferring method and the device arraying method, to form animage display portion. Accordingly, it is possible to efficientlyre-array the light emitting devices, which have been formed on the firstsubstrate densely, that is, with a high degree of integration, on thesecond substrate in such a manner as to be spaced from each other withan enlarged pitch, and hence to significantly improve the productivity.

According to an embodiment of the present invention, there is providedanother device transferring method of transferring devices arrayed on afirst substrate to a second substrate on which an adhesive layer ispreviously formed, the method including:

-   -   a heating step of selectively heating the adhesive layer on the        second substrate by irradiating those to be transferred of the        devices with laser beams passing through the second substrate,        thereby adhesively bonding the devices to be transferred to the        second substrate;    -   wherein a light absorbing material for increasing a light        absorptivity of the adhesive layer against the laser beams is        contained in the adhesive layer or disposed in the vicinity of        the adhesive layer.

With this device transferring method, portions, corresponding to devicesto be transferred, of the adhesive layer can be selectively heated, bylaser irradiation from the back surface side of the substrate, directlyor indirectly via the devices or wiring without heating portions, neardevices other than the devices to be transferred, of the adhesive layer.Also, since the light absorbing material for increasing the lightabsorptivity of the adhesive layer against laser beams is contained inthe adhesive layer or disposed in the vicinity of the adhesive layer,portions, corresponding to devices to be transferred, of the adhesivelayer are allowed to more desirably absorb the laser beams, and hence tobe more desirably heated. As a result, it is possible to efficiently,selectively heat the portions, corresponding to the devices to betransferred, of the adhesive layer.

Since the laser beams are absorbed by the light absorbing materialhaving the light absorptivity against the laser beams, the laser beamsdo not reach the devices to be transferred, so that it is possible toprevent the devices to be transferred from being damaged by the laserbeams. As a result, it is possible to select any kind and wavelength ofthe laser beam irrespective of the material of the device, that is, withthe damage of the device by the laser beam not taken into account.

By selecting a material having a known laser beam absorptioncharacteristic as the light absorbing material for increasing the lightabsorptivity of the adhesive layer against laser beams to be containedin the adhesive layer or disposed in the vicinity of the adhesive layer,it is possible to estimate the heat generation amount of the lightabsorbing material upon heating, and hence to select a material beingindependent of the laser beam absorption characteristic as the materialof the device.

According to an embodiment of the present invention, there is providedanother device arraying method of re-arraying a plurality of devicesarrayed on a first substrate to a second substrate, the methodincluding:

-   -   a first transferring step of transferring the devices from the        first substrate to a temporarily holding member in such a manner        that the devices are spaced from each other with a pitch larger        than a pitch of the devices arrayed on the first substrate and        holding the devices on the temporarily holding member;    -   a device isolation step of covering the devices held on the        temporarily holding member with a resin and isolating the        devices covered with the resin from each other;    -   an adhesive layer forming step of forming an adhesive layer        containing a light absorbing material for increasing a light        absorptivity against laser beams on the second substrate or        disposing the light absorbing material in the vicinity of the        adhesive layer; and    -   a second transferring step of selectively heating the adhesive        layer on the second substrate by irradiating those to be        transferred of the devices with laser beams passing through the        second substrate, thereby transferring those to be transferred        of the devices covered with the resin on the temporarily holding        substrate to the second substrate.

With this device arraying method, since portions, near the devices to betransferred, of the adhesive layer can be efficiently, certainly heatedby using the above-described device transferring method, it is possibleto efficiently and with certainty perform the transfer of the desireddevices and hence to smoothly perform enlarged transfer by means ofwhich the desired devices are transferred in such a manner as to bespaced from each other with an enlarged pitch.

According to an embodiment of the present invention, there is providedanother image display unit fabricating method of fabricating an imagedisplay unit including light emitting devices disposed in a matrix, themethod including:

-   -   a first transferring step of transferring the light emitting        devices from the first substrate to a temporarily holding member        in such a manner that the light emitting devices are spaced from        each other with a pitch larger than a pitch of the light        emitting devices arrayed on the first substrate and holding the        light emitting devices on the temporarily holding member;    -   a device isolation step of covering the light emitting devices        held on the temporarily holding member with a resin and        isolating the light emitting devices covered with the resin from        each other;    -   an adhesive layer forming step of forming an adhesive layer        containing a light absorbing material for increasing a light        absorptivity against laser beams on the second substrate or        disposing the light absorbing material in the vicinity of the        adhesive layer; and    -   a second transferring step of selectively heating the adhesive        layer on the second substrate by irradiating those to be        transferred of the light emitting devices with laser beams        passing through the second substrate, thereby transferring those        to be transferred of the light emitting devices covered with the        resin on the temporarily holding substrate to the second        substrate.

With this image display unit fabricating method, the light emittingdevices are arrayed in a matrix by making use of the above-describeddevice transferring method and the device arraying method, to form animage display portion. Accordingly, since portions, near the devices tobe transferred, of the adhesive layer can be efficiently, certainlyheated, it is possible to efficiently and with certainty perform thetransfer of the devices. This makes it is possible to efficientlyre-array the light emitting devices, which have been formed on the firstsubstrate densely, that is, with a high degree of integration, on thesecond substrate in such a manner as to be spaced from each other withan enlarged pitch, and hence to significantly improve the productivity.

According to an embodiment of the present invention, there is provided afurther device transferring method including:

-   -   a superimposing step of superimposing a second substrate having        a thermoplastic adhesive layer on a first substrate on which        devices are previously fixed in array via a thermal re-peelable        layer; and    -   a heating/cooling step of heating and cooling, in a state that        the devices are in contact with the thermoplastic adhesive        layer, the thermal re-peelable layer and the thermoplastic        adhesive layer, to make the devices peelable from the thermal        re-peelable layer and simultaneously melt and cure the        thermoplastic adhesive layer, thereby transferring the devices        to the second substrate.

With this device transferring method, the second substrate having thethermoplastic adhesive layer is superimposed on the first substrate onwhich devices are previously fixed in array via the thermal re-peelablelayer, and in a state that the devices are in contact with thethermoplastic adhesive layer, the thermal re-peelable layer and thethermoplastic adhesive layer are heated and cooled, to transfer thedevices from the first substrate to the second substrate.

Accordingly, in this device transferring method, the peeling of thedevices from the first substrate and the adhesive bonding of the devicesto the second substrate can be substantially simultaneously performedonly by the heating process.

According to an embodiment of the present invention, there is provided afurther device arraying method of re-arraying a plurality of devicesarrayed on a first substrate to a second substrate, the methodincluding:

-   -   a first transferring step of transferring the devices from the        first substrate to a temporarily holding member in such a manner        that the devices are spaced from each other with a pitch larger        than a pitch of the devices arrayed on the first substrate and        holding the devices on the temporarily holding member;    -   a covering step of covering the devices held on the temporarily        holding member with a resin;    -   a dicing step of dicing the resin so as to isolate the devices        from each other;    -   a second transferring step of transferring the resin-covered        devices held on the temporarily holding member to the second        substrate in such a manner that the resin-covered devices are        spaced from each other with a pitch larger than a pitch of the        resin-covered devices held on the temporarily holding member;    -   wherein the second transferring step includes:    -   a fixing step of fixing the resin-covered devices on a second        temporarily holding member via a thermal re-peelable layer;    -   a superimposing step of superimposing the second substrate        having a thermoplastic adhesive layer on the second temporarily        holding member; and    -   a heating/cooling step of heating and cooling, in a state that        the resin-covered devices are in contact with the thermoplastic        adhesive layer, the thermal re-peelable layer and the        thermoplastic adhesive layer, to make the resin-covered devices        peelable from the thermal re-peelable layer and simultaneously        melt and cure the thermoplastic adhesive layer, thereby        transferring the resin-covered devices to the second substrate.

With this device arraying method, since the devices can be efficientlyand with certainty performed by using the above-described devicetransferring method, it is possible to smoothly perform enlargedtransfer by means of which the desired devices are transferred in such amanner as to be spaced from each other with an enlarged pitch.

According to an embodiment of the present invention, there is provided afurther image display unit fabricating method of fabricating an imagedisplay unit including light emitting devices disposed in a matrix, themethod including:

-   -   a first transferring step of transferring the light emitting        devices from the first substrate to a temporarily holding member        in such a manner that the light emitting devices are spaced from        each other with a pitch larger than a pitch of the light        emitting devices arrayed on the first substrate and holding the        light emitting devices on the temporarily holding member;    -   a covering step of covering the light emitting devices held on        the temporarily holding member with a resin;    -   a dicing step of dicing the resin so as to isolate the light        emitting devices from each other;    -   a second transferring step of transferring the resin-covered        devices held on the temporarily holding member to the second        substrate in such a manner that the resin-covered devices are        spaced from each other with a pitch larger than a pitch of the        resin-covered devices held on the temporarily holding member;    -   wherein-the second transferring step includes:    -   a fixing step of fixing the resin-covered devices on a second        temporarily holding member via a thermal re-peelable layer;    -   a superimposing step of superimposing the second substrate        having a thermoplastic adhesive layer on the second temporarily        holding member; and    -   a heating/cooling step of heating and cooling, in a state that        the resin-covered devices are in contact with the thermoplastic        adhesive layer, the thermal re-peelable layer and the        thermoplastic adhesive layer, to make the resin-covered devices        peelable from the thermal re-peelable layer and simultaneously        melt and cure the thermoplastic adhesive layer, thereby        transferring the resin-covered devices to the second substrate.

With this image display unit fabricating method, the light emittingdevices are arrayed in a matrix by making use of the above-describeddevice transferring method and the device arraying method, to form animage display portion. Accordingly, since portions, near the devices tobe transferred, of the adhesive layer can be efficiently, certainlyheated, it is possible to efficiently, certainly perform the transfer ofthe devices. This makes it is possible to efficiently re-array the lightemitting devices, which have been formed on the first substrate densely,that is, with a high degree of integration, on the second substrate insuch a manner as to be spaced from each other with an enlarged pitch,and hence to significantly improve the productivity.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF FIGURES

FIGS. 1(a) and 1(b) are schematic sectional views showing a related artdevice transferring method.

FIG. 2(a) is a schematic view showing a state that an adhesive layer isformed on a base substrate and devices 3 are formed in array on the basesubstrate via the adhesive layer according to an embodiment of thepresent invention. FIG. 2(b) is a schematic view showing a state that atemporarily holding member is disposed opposite to the base substrateand is brought into press-contact therewith, and only necessary devicesare transferred to the temporarily holding member according to anembodiment of the present invention. FIG. 2(c) is a schematic viewshowing a state after the temporarily holding member is peeled from thebase substrate according to an embodiment of the present invention. FIG.2(d) is a schematic view showing a state that the temporarily holdingmember on which the devices have been transferred is disposed oppositeto a transfer substrate and is brought into press-contact therewith, andthe devices are transferred to the transfer substrate according to anembodiment of the present invention. FIG. 2(e) is a schematic viewshowing a state that excess portions of an adhesive layer are removed byetching, to accomplish the selective transfer process according to anembodiment of the present invention. FIG. 2(f) is a schematic viewshowing a state of the transfer substrate to which the devices have beenselectively transferred in such a manner as to be located among partsaccording to an embodiment of the present invention.

FIG. 3 is a schematic view showing a state that an adhesive resin layeris heated by laser beams according to an embodiment of the presentinvention.

FIG. 4 is a schematic view showing a state that the device is heated bylaser beams according to an embodiment of the present invention;

FIG. 5 is a schematic view showing a state that a wiring pattern isheated by laser beams according to an embodiment of the presentinvention.

FIGS. 6(a) to 6(d) are schematic views showing a device arraying methodaccording to an embodiment of the present invention, wherein FIG. 6(a)shows a state that devices such as light emitting devices are denselyformed on a first substrate, FIG. 6(b) shows a state that the devicesare transferred from the first substrate to a temporarily holding membershown by broken lines, FIG. 6(c) shows a state that the devices held onthe temporarily holding member are spaced from each other, and FIG. 6(d)shows a state that the devices in the form of resin-covered chips aretransferred to a second substrate in such a manner as to be enlargedlyspaced from each other.

FIG. 7 is a schematic perspective view of a resin-covered chip accordingto an embodiment of the present invention.

FIG. 8 is a schematic plan view of the resin-covered chip according toan embodiment of the present invention.

FIGS. 9(a) and 9(b) are a sectional view and a plan view showing oneexample of a light emitting device according to an embodiment of thepresent invention.

FIG. 10 is a schematic sectional view showing a first transferring stepaccording to an embodiment of the present invention.

FIG. 11 is a schematic sectional view showing an electrode pad formingstep according to an embodiment of the present invention.

FIG. 12 is a schematic sectional view showing another electrode padforming step performed after transfer of the devices to a secondtemporarily holding member according to an embodiment of the presentinvention.

FIG. 13 is a schematic sectional view showing an attracting stepaccording to an embodiment of the present invention.

FIG. 14 is a schematic sectional view showing a second transferring stepaccording to an embodiment of the present invention.

FIG. 15 is a schematic sectional view showing an insulating film formingstep according to an embodiment of the present invention.

FIG. 16 is a schematic sectional view showing a wiring forming stepaccording to an embodiment of the present invention.

FIG. 17 is a schematic view showing a state that a light absorbingmaterial for increasing a light absorptivity of an adhesive layeragainst laser beams is disposed and the device is heated by laser beamsaccording to an embodiment of the present invention.

FIGS. 18(a) to 18(c) are schematic sectional views showing one exampleof a transfer process according to an embodiment of the presentinvention, wherein FIG. 18(a) shows a state that the thermal re-peelablelayer is formed on a base substrate and a plurality of devices areformed in array on the base substrate via the thermal re-peelable layer,FIG. 18(b) shows a state that a transfer substrate is disposed in aspecific positional relationship with the base substrate and is broughtinto press-contact therewith, and FIG. 18(c) shows a state after thetransfer substrate is peeled from the base substrate.

FIG. 19 is a characteristic diagram showing a relationship between atemperature and a sticky force of a thermal peelable material accordingto an embodiment of the present invention.

FIG. 20 is a schematic view showing a state that the thermal re-peelablelayer and a thermoplastic adhesive layer are heated by laser beamsaccording to an embodiment of the present invention.

FIG. 21 is a schematic view showing a state that the devices are heatedby laser beams according to an embodiment of the present invention.

FIGS. 22(a) to 22(c) are sectional views showing one example of aprocess of transferring devices of one kind to a substrate, on whichdevices of another kind have been mounted, in accordance with anembodiment of the present invention, wherein FIG. 22(a) shows a statethat the devices are mounted on a thermoplastic adhesive layer in such amanner as to be spaced from each other at a specific pitch, FIG. 22(b)shows a state that a transfer substrate is disposed in a specificpositional relationship with a base substrate and is brought intopress-contact therewith, and FIG. 22(c) shows a state after the transfersubstrate is peeled from the base substrate.

FIG. 23 is a schematic sectional view showing a second transferring stepaccording to an embodiment of the present invention.

FIG. 24 is a schematic sectional view showing the second transferringstep according to an embodiment of the present invention.

FIG. 25 is a schematic sectional view showing one application example ofthe second transferring step according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to a device transferringmethods, device arraying methods and image display unit fabricatingmethods. More specifically, the present invention relates to devicetransferring methods of transferring devices, such as semiconductorlight emitting devices, and device arraying methods and image displayunit fabricating methods for transferring finely formed devices to awider region by using the device transferring method.

In an embodiment, the present invention provides device transferringmethod. As shown in FIG. 2(a), an adhesive layer 2 is formed on a basesubstrate 1 as a supply source, and a plurality of devices 3 are formedin array on the adhesive layer 2.

The devices 3 formed-on the adhesive layer 2 can be simply transferredto another substrate by using a sticky resin having a relatively smallsticky or adhesive force as an adhesive of the adhesive layer 2.

As the device 3, there can be used any type of device, examples of whichinclude a light emitting device, a liquid crystal control device, aphotoelectric transfer device, a piezoelectric device, a thin filmtransistor device, a thin film diode device, a resistance device, aswitching device, a micro-magnetic device, and a micro-optical device.

As shown in FIG. 2(b), a temporarily holding substrate (first substrate)4, which is taken as intermediate means of transfer, is placed oppositeto the base substrate 1 and is brought into press-contact therewith totransfer only desired devices 3 a from the base substrate 1 to thetemporarily holding substrate 4.

An adhesive layer is previously formed on the temporarily holdingsubstrate 4 such that adhesive layer portions 5 are selectively locatedat positions corresponding to those of the devices 3 a to betransferred. By making the sticky force of the adhesive layer portions 5larger than that of the adhesive layer 2 on the base substrate 1, thedevices 3 a can be simply transferred to the temporarily holdingsubstrate 4. FIG. 2(c) shows a state that the temporarily holdingsubstrate 4 has been peeled from the base substrate 1, wherein thedevices 3 a are left as transferred on the adhesive layer portions 5selectively formed on the temporarily holding substrate 4.

As shown in FIG. 2(d), the temporarily holding substrate 4 to which thedevices 3 a have been thus transferred is placed opposite to a transfersubstrate (second substrate) 6 and is brought into press-contacttherewith, to transfer the devices 3 a to the transfer substrate 6 side.It is to be noted that an adhesive layer 7 is previously formed on theoverall surface of the transfer substrate 6, wherein other parts 8 arealready fixed to the adhesive layer 7. The adhesive layer 7 is formed bycoating the surface of the transfer substrate 6 with, for example, athermoplastic adhesive resin. At the time of transfer of the devices 3a, it is required to partially irradiate the adhesive layer 7 with laserbeams from the back surface side of the transfer substrate 6.Accordingly, the transfer substrate 6 preferably has a lighttransmissivity.

The transfer of the devices 3 a to the transfer substrate 6 will be morefully described below. After the temporarily holding substrate 4 issuperimposed to the transfer substrate 6, the adhesive layer 7 ispartially irradiated with laser beams L from the back surface side ofthe transfer substrate 6, to selectively soften the adhesively layer 7,and then the selectively softened adhesive layer 7 is cooled to be thuscured, whereby the devices 3 are fixed to the adhesive layer 7.

For example, as shown in FIG. 3, only a portion, being in contact withthe device 3 a to be transferred, of the adhesive layer 7 is selectivelyirradiated with the laser beams L from the back surface side of thetransfer substrate 6, to be heated. As a result, only the heated regionH of the adhesive layer 7 made from a thermoplastic adhesive resin issoftened, to exhibit an adhesive force against the device 3 a. Theirradiation of the laser beams is then stopped, and the heated region His cooled to be cured, to fix the device 3 a to the transfer substrate 6via the adhesive layer 7.

At this time, portions, to which the other parts 8 have been adhesivelybonded, of the adhesive layer 7 are not irradiated with the laser beams,and thereby these portions of the adhesive layer 7 are not softened,with a result that only the desired devices 3 a can be transferredwithout occurrence of peeling or positional deviation of the parts 8.

In this embodiment, the heating of the adhesive layer 7 is performed bydirectly irradiating the adhesive layer 7 with the laser beams L;however, if the adhesive layer 7 less absorbs the laser beams L, thatis, if most of the laser beams L pass through the adhesive layer 7,thereby failing to directly heat the adhesive layer 7 with the laserbeams L, the device 3 a to be transferred may be irradiated, as shown inFIG. 4, with the laser beams L having passed through the adhesive layer7, to heat the device 3, thereby indirectly heating the adhesive layer7.

When the device 3 a to be transferred is irradiated with the laser beamsL and thereby a portion H, being in contact with the adhesive layer 7,of the device 3 a is heated, the heat is transmitted to a portion,corresponding to the device 3 a, of the adhesive layer 7, with a resultthat the portion, corresponding to the device 3 a, of the adhesive layer7 is softened. The softened portion of the adhesive layer 7 is thencooled to be cured, whereby the device 3 a is fixed to the transfersubstrate 6 via the adhesive layer 7.

In the case where a wiring portion is formed on the transfer substrate6, the wiring portion may be heated by laser irradiation, to indirectlyheat the adhesive layer 7.

FIG. 5 shows an example that a wiring pattern 9 is formed on thetransfer substrate 6 and the device 3 a is transferred on the wiringpattern 9. In general, the wiring pattern 9 for connecting the device 3a to a circuit is formed at a position corresponding to that of thewiring pattern 9. The wiring pattern 9 is made from a metal such ascopper or aluminum, and therefore, it can be easily heated by the laserbeams L.

As shown in FIG. 6, the wiring pattern 9 provided at a positioncorresponding to that of the device 3 a is irradiated with the laserbeams L, and thereby a region H, corresponding to the device 3 a, of thewiring pattern 9 is heated. The heat of the region H is transferred to aportion, corresponding to the device 3 a, of the adhesive layer 7, tosoften the portion, corresponding to the device 3 a, of the adhesivelayer 7. The softened portion of the adhesive layer 7 is then cooled tobe cured, whereby the device 3 a is fixed to the transfer substrate 6via the adhesive layer 7.

The heating manners shown in FIGS. 3, 4 and 5 may be performed singly orin combination. In the case of adopting the combination of the heatingmanners shown in FIGS. 3, 4 and 5, the portion, corresponding to thedevice 3 a, of the adhesive layer 71 is heated and softened by combiningdirect laser irradiation of the adhesive layer 7 with indirect laserirradiation of each of the device 3 a and the wiring pattern 9.

After the devices 3 a are fixed to the transfer substrate 6 via theadhesive layer 7 by selective heating due to laser irradiation,softening, and curing due to cooling, the temporarily holding substrate4 is peeled from the transfer substrate 6.

The devices 3 a to be transferred are thus transferred to the transfersubstrate 6. In this state, however, the adhesive layer 7 is left asbeing formed on the overall surface of the transfer substrate 6.

As shown in FIG. 2(e), unnecessary portions of the adhesive layer 7 areremoved by etching, to accomplish the selective transfer process.Consequently, the transfer substrate 6, to which the devices 3 a havebeen selectively transferred so as to be located among the parts 8 asshown in FIG. 2(f), can be obtained.

As described above, very narrow portions of the adhesive layer 7 can beheated for a short time by using laser beams. To be more specific, onlythe portion, corresponding to the devices 3 a, of the adhesive layer 7can be selectively heated without transfer of the heat to the adjacentportions, to which the parts 8 have been adhesively bonded, of theadhesive layer 7. As a results the devices 3 a can be selectivelytransferred without exerting any thermal effect on the fixed states ofthe parts 8 left as adhesively bonded adjacent to the devices 3 a.

If the adhesive layer 7 is overall heated as having been carried out bythe related art method, there may occur an inconvenience that theportions, to which the other parts 8 have been fixed, of the adhesivelylayer 7 be heated and fluidized, thereby tending to displace the parts8. Such an inconvenience can be solved by the present invention. Anotheradvantage of the present invention is as follows: namely, in the formingthe adhesive layer 7, it is not required to selectively coat only theportions, corresponding to the devices 3 a, of the transfer substrate 6with a small amount of the adhesive, but it is sufficient to coat theoverall surface of the transfer substrate 6 with the adhesive, andconsequently, it is possible to simplify the selective transfer process.

In an embodiment, the adhesive layer 7 is made from a thermoplasticadhesive resin; however, the adhesive layer 7 may be made from athermosetting adhesive resin. In the case of using the adhesive layer 7made from a thermosetting adhesive resin, only portions, correspondingto the devices 3 a, of the adhesive layer 7 may be heated by laserirradiation, to be thermally cured, thereby fixing the devices 3 a tothe transfer substrate 6 via the adhesive layer 7.

It is very useful to apply the above-described transfer method totransfer of devices in fabrication of an active matrix type imagedisplay unit. In an active matrix type image display unit, lightemitting devices of R, G, and B must be disposed adjacent to an Sitransistor as a drive device by sequentially transferring the lightemitting devices of R, G, and B to positions close to the Si transistor.In this transfer, however, since the Si transistor has a very highthermal conductivity, if heat is applied thereto, an inner circuitthereof may be broken. Such an inconvenience can be solved by theabove-described transfer method. That is to say, according to thistransfer method, the transfer of heat to the Si transistor can beavoided during the step of transferring the light emitting devices of R,G, and B.

Assuming that the Si transistor has a size of 560 μm×160 μm×35 μm, eachof the light emitting devices has a small area (one side: about 5 to 10μm), an epoxy based thermosetting resin is used as an adhesive resin ofan adhesive layer, and a YAG second harmonic laser (wavelength: 532 nm)is used as a laser source, it takes 1 nsec to heat portions,corresponding to the light emitting devices, of the adhesive layer bylaser irradiation and it takes about 10 nsec to cool the heated portionsof the adhesive layer. As long as it takes 4 nsec or less to heat theportions, corresponding to the light emitting devices, of the adhesivelayer by laser irradiation, the Si transistor adjacent thereto is notaffected by the heat generated by laser irradiation.

As an application example of the above-described transfer method, adevice arraying method and an image display unit fabricating methodbased on a two-step enlarged transfer method will be described belowaccording to an embodiment of the present invention. The two-stepenlarged transfer method applied to the device arraying method and theimage display unit fabricating method is carried out by forming deviceson a first substrate at a high density, transferring the devices to atemporarily holding member in such a manner that the devices are spacedfrom each other with a pitch larger than a pitch of the devices arrayedon the first substrate, and transferring the devices held on thetemporarily holding member to a second substrate in such a manner thatthe devices are spaced from each other with a pitch larger than thepitch of the devices held on the temporarily holding member. Althoughtwo-step transfer is adopted in this embodiment, multi-step transfersuch as three or more-step transfer can be adopted depending on arequired enlargement ratio between the pitch of the devices arrayed onthe first substrate and the pitch of the devices mounted on the secondsubstrate.

FIGS. 6(a) to 6(d) show basic steps of the two-step enlarged transfermethod.

As shown in FIG. 6(a), devices 12 such as light emitting devices aredensely formed on a first substrate 10. By densely forming devices on asubstrate, the number of devices formed per each substrate can beincreased, to reduce a final product cost thereof. The first substrate10 may be selected from substrates on each of which devices can beformed, for example, a semiconductor wafer, a glass substrate, a quartzglass substrate, a sapphire substrate, and a plastic substrate. Thedevices 12 may be directly formed on the first substrate 10, or may beformed once on another substrate, and then transferred to the firstsubstrate 10.

As shown in FIG. 6(b), the devices 12 are transferred from the firstsubstrate 10 to a temporarily holding member 11 shown by broken lines inthe figure, and held on the temporarily holding member 11. On thetemporarily holding member 11, the adjacent two of the devices 12 areenlargedly spaced from each other, and the devices 12 are arrayed in amatrix as a whole (see FIG. 6(b)). Specifically, the devices 12 aretransferred onto the temporarily holding member 11 in such a manner asto be enlargedly spaced from each other not only in the X direction butalso in the Y direction perpendicular to the X direction. The enlargeddistance between the adjacent two of the devices 12 on the temporarilyholding member 11 is not particularly limited, but may be determined,for example, in consideration of formation of resin portions andformation of electrode pads in the subsequent steps. The devices 12 onthe first substrate 10 can be all transferred from the first substrate10 to the temporarily holding member 11 in such a manner as to beenlargedly spaced from each other. In this case, a size of thetemporarily holding member 11 in each of the X direction and the Ydirection may be equal to or more than a value obtained by multiplyingthe enlarged distance by the number of those, arrayed in each of the Xdirection and the Y direction, of the devices 12 arrayed in the matrixon the temporarily holding member 11. In addition, part of the devices12 on the first substrate 10 may be transferred to the temporarilyholding member 11 in such a manner as to be enlargedly spaced from eachother.

After such a first transferring step, as shown in FIG. 6(c), each of thedevices 12 enlargedly spaced from each other on the temporarily holdingmember 11 is covered with a resin, and electrode pads are formed on theresin portion covering the device 11. The reason why each device 11 iscovered with the resin is to facilitate the formation of the electrodepads and to facilitate the handling of the device 11 in the subsequentsecond transferring step. To prevent occurrence of a wiring failure in afinal wiring step performed after the second transferring step (whichwill be described later), the electrode pads are formed into relativelylarge sizes. It is to be noted that the electrode pads are not shown inFIG. 6(c). A resin-covered chip 14 is thus formed by covering each ofthe devices 12 with a resin 13. The device 11 is located at anapproximately central portion of the resin-covered chip 14 in a planview in this embodiment; however, the device 11 may be located at aposition offset to one side or a corner of the resin-covered chip 14.

As shown in FIG. 6(d), a second transferring step is carried out. Inthis second transferring step, the devices 12 arrayed in the matrix onthe temporarily holding member 11 in the form of the resin-covered chips14 are transferred to a second substrate 15 in such a manner as to bemore enlargedly spaced from each other.

It is to be noted that as will be described in detail, the transfermethod shown in FIGS. 2(a) to 2(f) is applied to the second transferringstep.

Even in the second transferring step, adjacent two of the devices 12 inthe form of the resin-covered chips 14 are more enlargedly spaced fromeach other as compared with the first transferring step, to be arrayedin a matrix shown in the figure. Specifically, the devices 12 aretransferred in such a manner as to be more enlargedly spaced from eachother as compared with the first transferring step, not only in the Xdirection but also in the Y direction. If positions of the devices 12arrayed on the second substrate 15 in the second transferring stepcorrespond to positions of pixels of a final product such as an imagedisplay unit, a pitch of the devices 12 arrayed on the second substrate15 in the second transferring step becomes about integer times anoriginal pitch of the devices 12 arrayed on the first substrate 10.Assuming that an enlargement ratio between the pitch of the devices 12held on the temporarily holding member 11 and the pitch of the devices12 arrayed on the first substrate 10 is taken as “n” and an enlargementratio between the pitch of the devices 12 arrayed on the secondsubstrate 15 and the pitch of the devices 12 held on the temporarilyholding member 11 is taken as “m”, a value E of the above-describedabout integer times is expressed by E=n×m. The enlargement ratios “n”and “m” may be set to integers, but they may be not integers insofar asthey are selected such that the value E becomes an integer. For example,if the ratio “n” is set to 2.4 (not integer) and the ratio “m” is set to5 (integer), the value E becomes 12 (integer).

The devices 12 in the form of the resin-covered chips 14, which aresufficiently enlargedly spaced from each other on the second substrate15, are then subjected to wiring. The wiring is performed with caretaken not to cause a connection failure by making use of the previouslyformed electrode pads and the like. If the devices 12 are light emittingdevices such as light emitting diodes, the wiring includes wiring top-electrodes and n-electrodes. If the devices 12 are liquid crystalcontrol devices, the wiring includes wiring to selective signal lines,voltage lines, alignment electrode films, and the like.

In the two-step enlarged transfer shown in FIGS. 6(a) to 6(d), eachdevice 11 is covered with the resin and electrode pads are formed on theresin portion covering the device 11 by making use of the enlargeddistance between adjacent two of the devices 12 after the firsttransfer, and wiring can be performed after the second transfer withoutoccurrence of any connection failure by making use of the previouslyformed electrode pads and the like. As a result, it is possible toimprove a fabrication yield of the image display unit.

The two-step enlarged transfer method according to this embodimentincludes the two enlarged transfer steps in each of which the devicesare enlargedly spaced from each other. By performing a plurality of suchenlarged transfer steps in each of which the devices are enlargedlyspaced from each other, the number of transfer can be actually reduced.For example, assuming that an enlargement ratio between the pitch of thedevices 12 on the temporarily holding member 11 (11 a) and the pitch ofthe devices 12 on the first substrate 10 (10 a) is taken as 2 (n=2) andan enlargement ratio between the pitch of the devices 12 on the secondsubstrate 15 and the pitch of the devices 12 on the temporarily holdingmember 11 (11 a) is taken as 2 (m=2), the total enlargement ratiobecomes 2×2=4. To realize the total enlargement ratio (=4), according toa one-step transfer method, the number of transfer (alignment) of thedevices 12 from the first substrate 10 to the second substrate 15becomes 16 (=42). On the contrary, to realize the same total enlargementratio (=4), according to the two-step enlarged transfer method of thisembodiment, the number of transfer (alignment) is obtained by simplyadding a square of the enlargement ratio (=2) in the first transferringstep to a square of the enlargement ratio (=2) in the secondtransferring step, with a result that the number of transfer becomes 8(=4+4). Specifically, according to the two-step enlarged transfermethod, to achieve the total enlargement ratio (transfer magnification)of n×m, the total number of transfer becomes (n²+m²) times, whileaccording to the one-step transfer method, to achieve the same totalenlargement ratio (transfer magnification) of n×m, the number oftransfer becomes (n+m)²=n²+2 nm+m². As a result, according to thetwo-step enlarged transfer method, the number of transfer can be madesmaller than that according to the one-step transfer method by 2 nmtimes, thereby correspondingly saving time and cost required for thefabrication step. This becomes more useful as the total enlargementratio becomes large.

In the two-step enlarged transfer method shown in FIGS. 6(a) to 6(d),the device 12 is exemplified by a light emitting device; however, thedevice 12 is not limited thereto but may be selected from a liquidcrystal control device, a photoelectric transfer device, a piezoelectricdevice, a thin film transistor device, a thin film diode device, aresistance device, a switching device, a micro-magnetic device, amicro-optical device, and a combination thereof.

The device is handled as the resin-covered chip in the secondtransferring step, and is transferred from the temporarily holdingmember to the second substrate. Such a resin-covered chip will bedescribed with reference to FIGS. 7 and 8.

A resin-covered chip 20 is formed by covering each of devices 21 spacedfrom each other with a resin 22. The resin-covered chip 20 is usable intransfer of the device 21 from a temporarily holding member to a secondsubstrate as described above.

The resin-covered chip 20 is formed into an approximately flat plateshape with an approximately square shaped principal plane. The shape ofthe resin-covered chip 20 is equivalent to the shape of the cured resin22 covering the light emitting device 21. To be more specific, theresin-covered chips 20 are obtained by coating the overall surface of atemporarily holding member so as to cover the devices 21 with anon-cured resin 22, curing the resin 22, and cutting edge portions ofthe cured resin 22 into chips by dicing.

Electrode pads 23 and 24 are formed on front and back surface sides ofthe approximately flat plate like resin 22, respectively. Theseelectrode pads 23 and 24 are each produced by forming a conductive layermade from a metal or polysilicon as a material for forming each of theelectrode pads 23 and 24 overall on each of the front and back surfacesof the resin 22, and patterning the conductive layer into a specificelectrode shape by photolithography. These electrode pads 23 and 24 areformed so as to be connected to a p-electrode and an n-electrode of thedevice 21 as the light emitting device, respectively. If needed,via-holes may be formed in the resin 22.

In this embodiment, the electrode pads 23 and 24 are formed on the frontand back surface sides of the resin-covered chip 20, respectively;however, they may be formed on either of the front and back surfacesides of the resin-covered chip 20. If the device 21 is a thin filmtransistor having three electrodes, that is, source, gate, and drainelectrodes, three or more electrode pads may be formed. The reason whythe electrode pads 23 and 24 are offset from each other in thehorizontal direction is to prevent the electrode pads 23 and 24 frombeing overlapped to each other even if a contact hole is formed fromabove upon formation of final wiring. The shape of each of the electrodepads 23 and 24 is not limited to a square shape but may be any othershape.

The formation of such a resin-covered chip 20 is advantageous in thatsince the device 21 is covered with the flattened resin 22, theelectrode pads 23 and 24 can be accurately formed on the flattened frontand back surfaces of the resin 22, and the electrode pads 23 and 24 canbe formed so as to extend to a region wider than the size of the device21, thereby facilitating the handling of the device 21 at the time oftransfer by using an attracting jig in the second transferring step. Aswill be described later, since final wiring is performed after thesecond transferring step, a wiring failure can be prevented byperforming wiring by making use of the electrode pads 23 and 24 havingrelatively large sizes.

FIGS. 9(a) and 9(b) are a sectional view and a plan view, showing alight emitting device as one example of the device used for the two-stepenlarged transfer method according to an embodiment of the presentinvention.

The light emitting device shown in the figures is a GaN based lightemitting diode formed on a sapphire substrate by crystal growth. In sucha GaN based light emitting diode, when the light emitting diode isirradiated with laser beams having passed through the substrate, laserabrasion occurs, to evaporate nitrogen of GaN, thereby causing filmpeeling at the interface between the sapphire substrate and a GaN basedgrowth layer. As a result, the light emitting diodes can be easilypeeled from the sapphire substrate.

The structure of the GaN based light emitting diode will be describedbelow. A hexagonal pyramid shaped GaN layer 32 is formed by selectivegrowth on an under growth layer 31 composed of a GaN based semiconductorlayer. To be more specific, an insulating film (not shown) is formed onthe under growth layer 31, and the hexagonal pyramid shaped GaN layer 32is grown from an opening formed in the insulating film by a MOCVDprocess or the like. The GaN layer 32 is a growth layer having a pyramidshape covered with a S-plane, that is, (1-101) plane when a principalplane of the sapphire substrate used for growth is taken as a C-plane.The GaN layer 32 is a region doped with silicon. The tilt S-planeportion of the GaN layer 32 functions as a cladding portion of adouble-hetero structure. An InGaN layer 33 functioning as an activelayer is formed in such a manner as to cover the tilt S-plane of the GaNlayer 32. A GaN layer 34 doped with magnesium is formed on the InGaNlayer 33. The GaN layer 34 doped with magnesium also functions as acladding portion.

The light emitting diode has a p-electrode 35 and an n-electrode 36. Ametal material such as Ni/Pt/Au or Ni(Pd)/Pt/Au is vapor-deposited onthe GaN layer 34 doped with magnesium, to form the p-electrode 35. Ametal material such as Ti/Al/Pt/Au is vapor-deposited in an openingformed in the above-described insulating film (not shown), to form then-electrode 36. If an n-clectrode is extracted from the back surfaceside of the under growth layer 31 as shown in FIG. 11, the n-electrode36 is not required to be formed on the front surface side of the undergrowth layer 31.

The GaN based light emitting diode having such a structure allowsemission of blue light. In particular, the light emitting diode can berelatively simply peeled from the sapphire substrate by laser abrasion.In other words, the diode can be selectively peeled by selectiveirradiation of the diode with laser beams. The GaN based light emittingdiode may have a structure that an active layer be formed into a planaror strip shape, or may be a pyramid structure with a C-plane formed onan upper end portion of the pyramid. The GaN light emitting diode may bereplaced with any other nitride based light emitting device or acompound semiconductor device.

A concrete method of arraying the light emitting devices shown in FIGS.6(a) to 6(d) will be described below with reference to FIGS. 10 to 16.

The GaN based light emitting diode shown in FIGS. 9(a) and 9(b) is usedas the light emitting device. First, as shown in FIG. 10, a plurality oflight emitting diodes 42 are formed in a matrix on a principal plane ofa first substrate 41. A size of the light emitting diode 42 is set toabout 20 μm. The first substrate 41 is made from a material having ahigh transmittance for a wavelength of a laser beam used for irradiationof the light emitting diode 42, for example, made from sapphire. Thelight emitting diode 42 is already provided with a p-electrode and thelike but is not subjected to final wiring. Device isolation grooves 42 gare already formed, to make the light emitting diodes 42 isolatable fromeach other. The formation of the grooves 42 g may be made, for example,by reactive ion etching. As shown in FIG. 11, such a first substrate 41is placed opposite to a temporarily holding member 43 for selectivetransfer of the light emitting diodes 42 therebetween.

Both a peelable layer 44 and an adhesive layer 45 are formed on asurface, opposed to the first substrate 41, of the temporarily holdingmember 43. As the temporarily holding member 43, there can be used aglass substrate, a quartz glass substrate, or a plastic substrate. Thepeelable layer 44 on the temporarily holding member 43 can be made froma fluorine coat material, a silicone resin, a water soluble adhesive(for example, polyvinyl alcohol: PVA), polyimide and/or the like. Theadhesive layer 45 on the temporarily holding member 43 can be made froman ultraviolet (UV)-curing type adhesive, a thermosetting type adhesive,a thermoplastic type adhesive and/or the like. As one example, apolyimide film having a thickness of 4 μm is formed as the peelablelayer 44 on the temporarily holding member 43 made from quartz glass andan UV-curing type adhesive layer having a thickness of about 20 μm isformed as the adhesive layer 45 on the peelable layer 44.

The adhesive layer 45 provided on the temporarily holding member 43 isadjusted such that cured regions 45 s and non-cured regions 45 y aremixed in the adhesive layer 45. The first substrate 41 is positioned tothe temporarily holding member 43 such that the light emitting diodes 42to be selectively transferred are aligned to the non-cured regions 45 y.The adjustment of the adhesive layer 45 in such a manner that the curedregions 45 s and the non-cured regions 45 y are mixed in the adhesivelayer 45 may be performed by selectively exposing portions, spaced fromeach other with a pitch of 200 μm, of the UV-curing type adhesive layer45 by an exposure system, so that the portions, to which the lightemitting diodes 42 are to be transferred, of the adhesive layer 45remain non-cured and the other portions of the adhesive layer 45 arecured.

After such alignment, each of the light emitting diodes 42 to betransferred is irradiated with laser beams from the back surface side ofthe first substrate 41, and is then peeled from the first substrate 41by laser abrasion. Since the GaN based light emitting diode 42 isdecomposed into gallium and nitrogen at the interface between the GaNlayer and sapphire, the light emitting diode 42 can be relatively simplypeeled from the first substrate 41. The laser beam used for irradiationis exemplified by an excimer laser beam or a harmonic YAG laser beam.

The light emitting diode 42, which has been selectively irradiated witha laser beam, is peeled from the first substrate 41 at the interfacebetween the GaN layer and the first substrate 41 by laser abrasion, andis transferred to the opposed temporarily holding member 43 in such amanner that the p-electrode portion of the light emitting diode 42: ispieced in the corresponding non-cured region 45 y of the adhesive layer45. The other light emitting diodes 42, which are left as not irradiatedwith laser beams and also located at positions corresponding to those ofthe cured region 45 s of the adhesive layer 45, are not transferred tothe temporarily holding member 43. It is to be noted that only one lightemitting diode 42 is depicted as selectively irradiated with a laserbeam in FIG. 10; however, in actual, the light emitting diodes 42 spacedfrom each other with an n-pitch are similarly irradiated with laserbeams. With such selective transfer, the light emitting diodes 42 arearrayed on the temporarily holding member 43 in such a manner as to beenlargedly spaced from each other with a pitch larger than an originalpitch of the light emitting diodes 42 arrayed on the first substrate 41.

In the state that the light emitting diode 42 is held by the adhesivelayer 45 of the temporarily holding member 43, a back surface of thelight emitting diode 42, which is taken as an n-electrode side (cathodeelectrode side), is cleaned for removal of the resin (adhesive)therefrom. Accordingly, when an electrode pad 46 is formed on the backsurface of the light emitting diode 42, it can be electrically connectedthereto.

As one example of cleaning the back surface of the light emitting device42 to remove the adhesive resin of the adhesive layer 45 therefrom, theadhesive resin is etched with oxygen plasma, followed by cleaning byirradiation of UV ozone. In addition, when the GaN based light emittingdiode 42 is peeled from the first substrate 41 made from sapphire bylaser irradiation, gallium is deposited on the peeling plane. Such anelement must be etched, for example, by using an NaOH containing watersolution or dilute nitric acid. The electrode pad 46 is then patterned.At this time, the electrode pad 46 on the cathode side can be formedinto a size of about 60 μm square. As the electrode pad 46, there can beused a transparent electrode (ITO or ZnO based electrode) or aTi/Al/Pt/Au electrode. In the case of using-a transparent electrode,even if the electrode largely covers the back surface of the lightemitting diode 42, it does not shield light emission from the lightemitting diode 42. Accordingly, a patterning accuracy of the transparentelectrode may be rough and further the size of the electrode can be madelarge, to thereby facilitate the patterning process.

Referring to FIG. 12, after the light emitting diode 42 is transferredfrom the temporarily holding member 43 to a second temporarily holdingmember 47, a via-hole 50 on an anode electrode (p-electrode) side isformed in the adhesive layer 45 and an anode side electrode pad 49 isformed so as to be buried in the via-hole 50, and the adhesive layer 45made from the resin is diced. As a result of dicing, device isolationgrooves 51 are formed, to make the light emitting diode 42 isolatablefrom those adjacent thereto. To isolate the light emitting diodes 42arrayed in a matrix from each other, the device isolation grooves 51have a planar pattern composed of pluralities of parallel linesextending in the vertical and horizontal directions. The bottom of thedevice isolation groove 51 faces to a surface of the second temporarilyholding member 47.

A peelable layer 48 is previously formed on the second temporarilyholding member 47. The peelable layer 48 is typically made from afluorine coat material, silicone resin, a water soluble resin (forexample, PVA), or polyimide. The second temporarily holding member 47 isexemplified by a so-called dicing sheet formed by coating a plasticsubstrate with an UV sticky material, wherein the sticky force of thesheet is lowered by irradiating the sticky material with UV.

The peelable layer 48 is irradiated with excimer laser beams from theback surface side of the temporarily holding member 47. As a result, ifthe peelable layer 44 is made from polyimide, peeling occurs at theinterface between polyimide and the quartz substrate by abrasion ofpolyimide, so that the light emitting diode 42 can be transferred to thesecond temporarily holding member 47 side.

As one example of the above process of forming the anode side electrodepad 49, the surface of the second temporarily holding member 47 isetched by oxygen plasma until the surface of the light emitting diode 42is exposed. The formation of the via-hole 50 having a diameter of about3 to 7 μm can be made by air excimer laser beam, a harmonic YAG laserbeam, or a carbon dioxide laser beam. The anode side electrode pad 49 isformed by, for example, Ni/Pt/Au. The dicing process is performed byusing a usual blade, and if a narrow cut-in width of 20 μm or less isneeded, the dicing process may be performed by using the above-describedlaser beam. The cut-in width is dependent on the size of a resin-coveredchip, formed by covering the light emitting diode 42 with the adhesivelayer 45 made from the resin, within a pixel of the final image displayunit. As one example, the device isolation grooves having the cut-inwidth of about 40 μm are formed by an excimer laser beam, to form eachresin-covered chip.

The light emitting diode 42 is peeled from the second temporarilyholding member 47 by using mechanical means. FIG. 13 is a view showing astate that each of the light emitting diodes 42 arrayed on the secondtemporarily holding member 47 is picked up by means of an attractingsystem 53. The attracting system 53 has attracting holes 55 opened in amatrix with a pitch corresponding to a pixel pitch of an image displayunit in order to collectively attract a number of the light emittingdiodes 42. The attracting holes 55, each having an opening diameter ofabout 100 μm, are arrayed into a matrix with a pitch of about 600 μm, sothat the attracting system 53 can collectively attract 300 pieces of thelight emitting diodes 42. As a member having the attracting holes 55,there may be used a member produced from Ni by electrocasting or a metalplate 52 such as a SUS plate, wherein the member formed by casting orthe metal plate 52 is perforated by etching. An attracting chamber 54 isformed at the depth of the attracting hole 55 formed in the metal plate52. By controlling the pressure in the attracting chamber 54 into anegative pressure, the attracting system 53 can attract the lightemitting diode 42. Since each light emitting diode 42 is in a statebeing covered with the adhesive layer 45 with its upper surface nearlyflattened, the selective attraction of the light emitting diode 42 bythe attracting system 53 can be easily performed.

FIG. 14 is a view showing a state that the light emitting diode 42 istransferred to a second substrate 60 by using the above-describedtransfer method shown in FIG. 2(a) to FIG. 5. An adhesive layer 56 ispreviously formed on the second substrate 60 before the light emittingdiode 42 is transferred to the second substrate 60. By curing a portion,located on the back surface of the light emitting diode 42, of theadhesive layer 56, the light emitting diode 42 is fixed on the secondsubstrate 60. Upon this mounting, the pressure of the attracting chamber54 of the attracting system 53 becomes high, to release the couplingstate between the light emitting diode 42 and the attracting system 53by attraction.

The adhesive layer 56 is made from a thermosetting adhesive or athermoplastic adhesive.

The light emitting diodes 42 thus arrayed on the second substrate 60 areenlargedly spaced from each other with a pitch larger than the pitch ofthe light emitting diodes 42 held on the first temporarily holdingmember 43 and also larger than the pitch of the light emitting diodes 42held on the second temporarily holding member 47. An energy (laser beam73) for curing the resin of the adhesive layer 56 is given from the backsurface of the second substrate 60.

As described above, only a portion, corresponding to the light emittingdiode 42 in the form of the resin-covered chip (light emitting diode 42covered with the adhesive layer 45), of the adhesive layer 56 isirradiated with laser beams 73 from the back surface side of the secondsubstrate 60, to be heated. If the adhesive layer 56 is made from athermoplastic adhesive, the heated portion of the adhesive layer 56 issoftened, and is cooled to be cured, whereby the resin-covered chip isfixed to the second substrate 60. Similarly, if the adhesive layer 56 ismade from a thermosetting adhesive, only the portion, irradiated withthe laser beams 73, of the adhesive layer 56 is cured, whereby theresin-covered chip is fixed to the second substrate 60.

An electrode layer 57 serving as a shadow mask may be disposed on thesecond substrate 60. In this case, by irradiating a portion,corresponding to the above target portion of the adhesive layer 56, ofthe electrode layer 57 with the laser beams 73 so as to heat the portionof the electrode layer 57, the target portion of the adhesive layer 56can be indirectly heated. In particular, a black chromium layer 58 maybe formed on a surface, on the screen side, that is, on the viewer side,of the electrode layer 57. With this provision of the black chromiumlayer 58, it is possible to improve the contrast of an image, and alsoto increase an energy absorptivity of the electrode layer 57 via theblack chromium layer 58 and hence to efficiently heat the target portionof the adhesive layer 56 by selectively irradiated laser beams 73.

FIG. 15 is a view showing a state that light emitting diodes 42, 61, and62 of three colors, RGB are arrayed on the second substrate 60 and arecoated with an insulating layer 59. The light emitting diodes 42, 61,and 62 can be respectively mounted on the second substrate 60 atpositions offset from each other in the order of the three colors byusing the attracting system 53 shown in FIGS. 13 and 14, whereby a pixelcomposed of the light emitting diodes 42, 61 and 62 of RGB can be formedwith a pixel pitch fixed. The insulating layer 59 may be made from atransparent epoxy adhesive, UV-curing type adhesive, or polyimide. Theshapes of the light emitting diodes 42, 61, and 62 of the three colorsare not necessarily identical to each other. In the example shown inFIG. 15, the red light emitting diode 61 has a structure having nohexagonal pyramid shaped GaN layer, and is different in shape from eachof the other light emitting diodes 42 and 62; however, since in thisstage, each of the light emitting diodes 42, 61, and 62 has been alreadycovered with the adhesive layer 45 to be formed into a resin-coveredchip, the light emitting diodes 42, 61, and 62 can be handled in thesame manner irrespective of the difference in device structure.

FIG. 16 is a view showing a wiring formation step. Opening portions 65,66, 67, 68, 69, and 70 are formed in the insulating layer 59, and wiringportions 63, 64 and 71 for connecting the electrode pads for the anodeand cathode of each of the light emitting diodes 42, 61 and 62 to theelectrode layer 57 for wiring on the second substrate 60 are formed inthe opening portions 65, 66, 67, 68, 69 and 70. Since the areas of theelectrode pads 46 and 49 of each of the light emitting diodes 42, 61,and 62 are large, the shapes: of the opening portions, that is,via-holes can be made large. As a result, each via-hole can be formedwith a rough positioning accuracy as compared with a via-hole directlyformed in each light emitting diode. For each of the electrode pads 46and 49 having a size of about 60 μm square, the via-hole having adiameter of about 20 μm can be formed. The via-holes are of three kindshaving different depths: the first kind is connected to the wiringsubstrate, the second kind is connected to the anode electrode, and thethird kind is connected to the cathode electrode. The depth of eachvia-hole is optimized by controlling the pulse number of a laser beamdepending on the kind of the via-hole. A protective layer is then formedon the wiring, to accomplish a panel of an image display unit. Theprotective layer-may be made from the same transparent epoxy adhesive asthat used for the insulating layer 59 shown in FIG. 17. The protectivelayer is heated to be cured, to perfectly cover the wiring. A driver ICis then connected to the wiring at the end portion of the panel, toproduce a drive panel.

In the above-described method of arraying light emitting devicesaccording to an embodiment of the present invention, since the lightemitting diodes 42 are already enlargedly spaced from each other whenbeing held on the temporarily holding member 43, the relatively largeelectrode pads 46 and 49 can be provided by making use of the largedistance between adjacent two of the light emitting diodes 42.

Since the wiring is performed by making use of the relatively largeelectrode pads 46 and 49, even if the size of the final unit issignificantly larger than the device size, the wiring can be easilyformed. According to the method of arraying light emitting devices inthis embodiment, since each light emitting device 42 is covered with theflattened cured adhesive layer 45, the electrode pads 46 and 49 can beaccurately formed on the front and back surfaces of the flattenedadhesive layer 45 and can be also disposed to extend to a region widerthan the device size, so that the handling of the light emitting device42 by the attracting jig in the second transferring step can befacilitated. In the transfer of the light emitting diode 42 to thetemporarily holding member 43, the light emitting diode 42 can berelatively simply peeled to be certainly transferred by making use thephenomenon that GaN material is decomposed into gallium and nitrogen atthe interface between the GaN material and sapphire. Since the transfer(second transferring step) of the resin-covered chip to the secondsubstrate is performed by selectively heating the adhesive layer bylaser irradiation and curing the adhesive layer, only the resin-coveredchip to be transferred can be certainly transferred without exerting anyeffect on the adhesive state of other parts.

An embodiment, which carries out each of the device transferring method,the device arraying method, and the image display unit fabricatingmethod according to the present invention, will be described below. Asreferred to below, parts corresponding to those parts previouslydescribed-are denoted by the same reference numerals and therefore thedetailed description thereof is omitted.

In an embodiment, an adhesive layer equivalent to the adhesive layer 7described above contains a light absorbing material for increasing alight absorptivity of the adhesive layer against laser beams.

The light absorbing material for increasing a light absorptivity of theadhesive layer may be disposed in the vicinity of the adhesive layer. Assuch a light absorbing material contained in the adhesive layer ordisposed in the vicinity of the adhesive layer, there may be used ametal thin film made from chromium or aluminum, or a particulatematerial such as carbon black or calcium carbonate. If a light absorbingmaterial for increasing a light absorptivity of an adhesive layeragainst laser beams is used in the form of a metal thin film, the metalthin film may be formed on the surface, to be adhesively bonded to theadhesive layer, of a device to be transferred, or formed on the surface,to be adhesively bonded to the device, of the adhesive layer. Meanwhile,if a light absorbing material is used in the form of a particulatematerial, the particulate material may be contained in the adhesivelayer, or formed on the surface, to be adhesively bonded to the adhesivelayer, of a device.

In the device transferring method according to the first embodiment, asshown in FIG. 3, a portion, being in contact with the device 3 a to betransferred, of the adhesive layer 7 is selectively irradiated with thelaser beams L from the back surface side of the transfer substrate 6 tobe heated, whereby the heated region H of the adhesive layer 7 made froma thermoplastic adhesive resin is cured to exhibit an adhesive forceagainst the device 3 a. In this laser irradiation, according to thesecond embodiment, since the adhesive layer 7 contains a light absorbingmaterial 7 a for increasing a light absorptivity of the adhesive layer 7against the laser beams L, the portion, corresponding to the device 3 a,of the adhesive layer 7 efficiently absorbs the laser beams L, to bethus desirably heated. As a result, it is possible to efficiently,selectively heat the portion, corresponding to the device 3 a to betransferred, of the adhesive layer 7. In this way, according to thisembodiment, the presence of the light absorbing material 7 a allows theportion, corresponding to the device 3 a, of the adhesive layer 7 to beefficiently, selectively heated.

The presence of the light absorbing material 7 a has another advantagethat since the laser beams L are absorbed by the light absorbingmaterial 7 a for increasing a light absorptivity of the adhesive layer 7against the laser beans L, and therefore, the laser beams L do not reachthe device 3 a, it is possible to prevent the device 3 a from beingdamaged by the laser beams L.

After the irradiation of the laser beams L is stopped, the heated regionH of the adhesive layer 7 is cooled to be cured, whereby the device 3 ais fixed to the transfer substrate 6 via the adhesive layer 7. At thistime, since the adhesive layer 7 contains the light absorbing material 7a for increasing a light absorptivity of the adhesive layer 7 againstthe laser beams L, the laser beams L are absorbed by the light absorbingmaterial 7 a, with a result that the portion, corresponding to thedevice 3 a, of the adhesive layer 7 can be efficiently, selectivelyheated.

The adhesive layer 7 containing the light absorbing material 7 a forincreasing a light absorptivity of the adhesive layer 7 against thelaser beams L can be performed in another manner. In the devicetransferring method according to the first embodiment, as shown in FIG.3, the device 3 a to be transferred is irradiated with the laser beams Lhaving passed through the adhesive layer 7, to indirectly heat theportion, corresponding to the device 3 a, of the adhesive layer 7. Inthis laser irradiation manner, according to the second embodiment, sincethe light absorbing material 7 a for increasing a light absorptivity ofthe adhesive layer 7 against the laser beams is contained in theadhesive layer 7 (or disposed in the vicinity of the adhesive layer 7),the laser beams L are absorbed by the light absorbing material 7 ahaving a light absorptivity against the laser beams. L, with a resultthat the laser beams L do not reach the device 3 a, thereby preventingthe device 3 a from being damaged by the laser beams L.

Even in the case of indirectly heating the portion, corresponding to thedevice 3 a to be transferred, of the adhesive layer 7 by irradiating theportion H, being in contact with the adhesive layer 7, of the device 3 awith the laser beams L so as to heat the portion H or by irradiating awiring portion formed on the transfer substrate 6 with the laser beams Lso as to heat the wiring portion, since the laser beams L are absorbedby the light absorbing material 7 a for increasing a light absorptivityof the adhesive layer 7, with a result that the laser beams L do notreach the device 3 a, thereby preventing the device 3 a from beingdamaged from the laser beams L.

Since the light-absorbing material having a light absorptivity againstthe laser beams L prevents the laser beams L from reaching the device 3a, the laser beams L do not reach the device 3 a. As a result, it ispossible to freely select the kind and wavelength of the laserirrelevant to the material of the device 3 a without taking into accountthe fact that the device 3 a is damaged by the laser beams L.

By selecting a material having a known absorption characteristic againstthe laser beams L as the light absorbing material 7 a for increasing alight absorptivity of the adhesive layer 7 against the laser beams, itis possible to estimate a heat generation amount upon heating by laserirradiation, and to select the material irrelevant to the absorptioncharacteristic against the laser beams L as the material of the device 3a.

Although the description has been made by way of the example that theadhesive layer 7 is made from a thermoplastic adhesive layer, theselective transfer of devices can be performed in the same manner asthat described above even if the adhesive layer 7 is made from athermosetting adhesive resin. In the case of using the adhesive layer 7made from a thermosetting resin, a portion, irradiated with the laserbeams L, of the adhesive layer 7 is thermally cured, to fix the deviceto the transfer substrate.

FIG. 17 shows a state that the light absorbing material 7 a forincreasing a light absorptivity of the adhesive layer 7 against thelaser beams L is disposed on the surface, on the adhesive layer 7 side,of the device 3 a to be transferred, to heat the portion, correspondingto the device 3 a, of the adhesive layer 7. Even in this case, like thecase where the light absorbing material 7 a is contained in the adhesivelayer 7, the laser beams L are absorbed by the light absorbing material7 a having a high light absorptivity against the laser beams L, with aresult that the laser beams L do not reach the device 3 a or the wiringportion, thereby preventing the device 3 a or the wiring portion frombeing damaged by the laser beams L.

A device arraying method and an image display unit fabricating methodusing the above-described device transferring method according to anembodiment of the present invention will be described below. Thetwo-step enlarged method used for the device arraying method and theimage display unit fabricating method are the same as previouslydescribed, and therefore, the overlapped description thereof is omitted.

In an embodiment, in the concrete method of arraying light emittingdevices shown in FIGS. 10 to 16, a light absorbing material forincreasing a light absorptivity against laser beams is contained in eachof the adhesive layers 45 and 56.

According to the device arraying method and the image display unitfabricating method in an embodiment, in the step of transferring thelight emitting diode 42 to the second substrate 60, the adhesive layer56 shown in FIG. 14 can be made from a thermosetting adhesive or athermoplastic adhesive, and contains a light absorbing material 56 a forincreasing a light absorptivity of the adhesive layer 56 against thelaser beams L. As the light absorbing material 56 a contained in theadhesive layer 56, there may be used calcium carbonate, carbon or otherlike materials.

Here, the adhesive layer 56 can be made from a thermosetting adhesive ora thermoplastic adhesive, and contains a light absorbing material 56 afor increasing a light absorptivity of the adhesive layer 56 against thelaser beams L. As the light absorbing material 56 a contained in theadhesive layer 56, there may be used calcium carbonate, carbon or thelike.

The light emitting diodes 42 arrayed on the second substrate 60 areenlargedly spaced from each other with a pitch larger than the pitch ofthe light emitting diodes 42 held on the first temporarily holdingmember 43 and also larger than the pitch of the light emitting diodes 42held on the second temporarily holding member 47. An energy for curingthe resin of the adhesive layer 56 is given from the back surface of thesecond substrate 60.

As described above, only a portion, corresponding to the light emittingdiode 42 in the form of the resin-covered chip (light emitting diode 42covered with the adhesive layer 45), of the adhesive layer 56 isirradiated with the laser beams 73 from the back surface side of thesecond substrate 60, to be heated. If the adhesive layer 56 is made froma thermoplastic adhesive, the heated portion of the adhesive layer 56 issoftened, and is cooled to be cured, whereby the resin-covered chip isfixed to the second substrate 60. Similarly, if the adhesive layer 56 ismade from a thermosetting adhesive, only the portion, irradiated withthe laser beams 73, of the adhesive layer 56 is cured, whereby theresin-covered chip is fixed to the second substrate 60.

In this case, by irradiation of the laser beams 73 from the back surfaceside of the second substrate 60, the portion, corresponding to the lightemitting diode 42, of the adhesive layer 56 can be selectively heateddirectly or indirectly via the light emitting diode 42 and the electrodelayer 57 without heating the portions, near the light emitting diodesnot to be transferred, of the adhesive layer 56. Further, by containingthe light absorbing material 56 a for increasing a light absorptivity ofthe adhesive layer 56 against the laser beams 73 in the adhesive layer56, the laser beams 73 can be more desirably absorbed in the portion,corresponding to the light emitting device 42, of the adhesive layer 56.As a result, it is possible to efficiently, selectively heat theportion, corresponding to the light emitting diode 42, of the adhesivelayer 56.

In the above-described method of arraying light emitting diodes, sincethe device transferring method according to the second embodiment isused, that is, since the light absorbing material 56 a for increasing alight absorptivity of the adhesive layer 56 against the laser beams 73is contained in the adhesive layer 56, it is possible to efficiently,selectively heat the portion, corresponding to each light emitting diode42 to be transferred, of the adhesive layer 56, and hence to efficientlyarray the light emitting diodes 42.

The presence of the light absorbing material 56 a for increasing a lightabsorptivity of the adhesive layer 56 against the laser beams 73 hasanother advantage that since the laser beams 73 are absorbed by thelight absorbing material 56 a and therefore the laser beams 73 do notreach the light emitting diode 42, with a result that the light emittingdiode 42 is prevented from being damaged by the laser beams 73. As aresult, it is possible to array the light emitting diodes 42 withoutdamaging the light emitting diodes 42 by the laser beams 73.

In the device transferring method according to an embodiment, since thekind of the laser beam is not dependent on the material of the device tobe transferred, it is possible to freely select the kind of the laser,and since the light absorbing material 56 a for increasing a lightabsorptivity of the adhesive layer 56 can be simply provided bycontaining the light absorbing material 7 a in the adhesive layer 56 andcoating the overall surface of the second substrate 60 with the adhesivelayer 56, it is possible to array the light emitting diodes 42 by asimple process.

A further advantage of the device transferring method according to anembodiment is that since the time required for irradiating each lightemitting diode 42 to be transferred with the laser beams 73 is shortbecause of efficient heating-the-portion, corresponding to the lightemitting diode 42, of the adhesive layer 56 and the portions,corresponding to the light emitting diodes not to be transferred, of theadhesive layer 56 are not heated, the light emitting diodes 42 to betransferred can be certainly, accurately arrayed without exertingadverse effect on the fixed states of the other light emitting diodes,that is, without peeling and positional deviation of the light emittingdiodes other than the light emitting diodes 42 to be transferred.

An embodiment, which carries out each of the device transferring method,the device arraying method, and the image display unit fabricatingmethod according to the present invention, will be described below. Asreferred to below, parts corresponding to those parts previouslydescribed are denoted by the same reference numerals and therefore thedetailed description thereof is omitted.

A device transferring method according to an embodiment of the presentinvention will be described below. To transfer devices 3 in accordancewith the device transferring method of the present invention, as shownin FIG. 18(a), a thermal re-peelable layer 81 is formed on a basesubstrate 1 as a supply source, and a plurality of devices are formed inarray on the base substrate 1.

The thermal re-peelable layer 81 has a property that the sticky forcethereof is reduced when the layer 81 is heated. The thermal re-peelablelayer 81 having such a property makes a member adhesively bonded to thelayer 81 re-peelable therefrom. Accordingly, in the case of forming thethermal re-peelable layer 81 on the base substrate 1 and forming thedevices 3 in array on the thermal re-peelable layer 81, the devices 3can be simply transferred to another substrate.

As the thermal re-peelable layer 81, there can be desirably used a sheetmade from a thermoplastic resin or a thermal peelable material. In thecase of using a thermoplastic resin as the material of the thermalre-peelable layer 81, the thermoplastic resin is plasticized when thethermal re-peelable layer 81 is heated, to reduce an adhesive forcebetween the thermal re-peelable layer 81 and each device 3, whereby thedevice 3 can be easily peeled from the thermal re-peelable layer 81. Inthe case of using a thermal peelable resin as the material of thethermal re-peelable layer 81, as shown in FIG. 19, a sticky force of thethermal peelable material is rapidly reduced at a specific temperature,whereby the device 3 can be easily peeled from the thermal re-peelablelayer 81. The temperature at which the sticky force of the thermalpeelable material is rapidly reduced, that is, a temperature T shown inFIG. 19 differs depending on the kind of the thermal peelable material,and for example, the temperature T ranges from 80° C. to 170° C.

The thermal peelable material is a material capable of reducing itssticky force by a foaming or expansion treatment due to heating, therebymaking a member adhesively bonded to the material simply peelabletherefrom. Specifically, when the thermal peelable material is heated, afoaming agent or an expanding agent contained in the material is foamedor expanded, to reduce the sticky area of the material, thereby losingthe sticky force of the material. For example, a heating re-peelabletype sticky sheet composed of a base material and a sticky layercontaining a foaming agent provided thereon is disposed, for example, inJapanese Patent Laid-open Nos. Sho 50-13878 and Sho 51-24534, andJapanese Patent Laid Publication Nos. Sho 56-61468, Sho 56-61469, andSho 60-252681. A heating peelable type sticky sheet composed of athermal expandable layer containing thermal expandable micro-balls andthereby being expandable by heating and a non-expandable sticky layerprovided at least one surface of the thermal expandable layer isdisclosed, for example, in Japanese Patent Laid-open No. 2000-248240. Aheating peelable type sticky sheet configured such that a thermalexpandable layer containing thermal expandable micro-balls and a stickylayer containing a sticky material are provided at least on one surfaceof a base material having a heat resistance and a flexibility isdisclosed, for example, in Japanese Patent Laid-open No. 2000-169808.

In the above-described heating peelable type sticky sheets, the thermalexpandable layer containing thermal expandable micro-balls acts asfollows: namely, when heated, the thermal expandable layer is expandedand thereby the surface thereof is irregularly deformed, with a resultthat the surface of the sticky layer provided on the thermal expandablelayer is correspondingly irregularly deformed, to reduce the adhesiveforce thereof against a member adhesively thereto. Accordingly, themember adhesively bonded to the heating peelable type sticky sheet canbe simply peeled therefrom at any time by heating the thermal expandablelayer of the heating peelable type sticky sheet.

The thermal expandable layer can be formed by mixing thermal expandablemicro-balls with a binder. The binder is exemplified by a polymer or awax allowing foaming and/or expansion of the thermal-expandablemicro-balls due to heating. In particular, from the viewpoint ofcontrolling the heating expansion characteristic of thermal expandablemicro-balls and the sticking characteristic such as a sticky forceagainst a member bonded to a sticky layer via the sticky layer, asticker is preferably used as the binder. The sticker is notparticularly limited but may be selected from polymers such as a rubberbased polymer, an acrylic based polymer, a vinyl alkyl ether basedpolymer, a silicone based polymer, a polyester based polymer, apolyamide based polymer, an urethane based polymer, a fluorine basedpolymer, and a styrene-diene copolymer. Such a polymer may be added witha thermally molten resin having a melting point of about 200° C. or lessfor improving the creep characteristic of the polymer. The sticker maybe an ultraviolet-curing type polymer. The above polymer used for thesticker may be further added with one or more additives such as acrosslinking agent, a tackifier, a plasticizer, a softener, a filler, apigment, a coloring agent, an antioxidant, and a surface active agent.

As the thermal expandable micro-balls contained in the thermalexpandable layer, there may be used micro-capsules formed by enclosing amaterial easily gasified to exhibit a thermal expansion characteristic,such as isobutane, propane, or pentane in shells made from a shellforming material by a coagervation method or an interfacialpolymerization method. As the shell forming material, there may be useda thermally molten material or a material allowed to be broken bythermal expansion, for example, vinylidene chloride-acrylonitrilecopolymer, polyvinyl alcohol, polyvinyl butyral, polymethylmethacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfoneand/or the like. The average particle size and the content of thethermal expandable micro-balls may be suitably set in accordance with anexpansion magnification of the thermal expandable layer and the degreeof reduction in sticky force.

The base material of the heating peelable type sticky sheet functions asa support for the thermal expandable sticky layer and the like, and isconfigured as a material having a flexibility and a heat resistancebeing large enough to keep the mechanical properties even by thetreatment of heating the thermal expandable sticky layer. The basematerial is exemplified by a heat stabilizer containing soft polyvinylchloride film or sheet, an expandable polyester film or sheet, a softpolyolefine film or sheet, a rubber base polymer sheet, or a multi-layerfilm or sheet including the above films or sheets.

The elongation percentage after fracture of the film or sheet formingthe base material, specified under JIS K7113 (for sheet) or JIS K7127(for film), is generally in a range of about 100% or more, preferably,in a range of 250% or more. The upper limit of the elongation percentageafter fracture is not particularly limited. The thickness of the basematerial may be freely selected insofar as it does not obstruct theworkability.

The thermal expandable sticky layer contains a sticky material forgiving stickiness, and thermal expandable micro-balls for giving athermal expansion characteristic. As the sticky material, there may beused a general sticker or adhesive, for example, a thermal activationtype sticker, a water or organic solvent activation type sticker, or apressure-sensitive sticker.

The sticky layer may contain, in addition to the sticky material, one ormore additives, for example, a crosslinking agent such as an isocyanatebased crosslinking agent or an epoxy based crosslinking agent, atackifier such as a resin derivative resin, a polyterpene resin, apetroleum resin, or an oil soluble resin, a plasticizer, a filler, andan antioxidant.

The thermal expandable micro-balls contained in the thermal expandablesticky layer may be micro-balls formed by enclosing a material easilygasified by heating to exhibit the thermal expansion characteristic suchas isobutane, propane, or pentane in an elastic shell. The shell is madefrom a thermoplastic material, a thermal molten material, or a materialallowed to be broken by thermal expansion. Examples of such a shellforming material include vinylidene chloride-acrylonitrile copolymer,polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate,polyacrylonitrile, polyvinylidene chloride, or polysulfone. The thermalexpandable micro-balls can be produced by a usual method such as acoagervation method or an interfacial polymerization method.

The average particle size of the thermal expandable micro-balls ispreferably in a range of 1 to 50 μm from the viewpoint of itsdispersibility or thin layer formability. To efficiently reduce thesticky force of the sticky layer containing a sticky material byheating, the strength of the thermal expandable micro-balls ispreferably large enough to prevent the breakage of the micro-balls untilthe volume expansion magnification thereof becomes 5 times or more,particularly, 10 times or more.

The content of the thermal expandable micro-balls is dependent on thekind thereof, and is generally in a range of 10 to 200 parts by weight,preferably, 25 to 125 parts by weight on the basis of the 100 parts byweight of the base polymer forming the thermal expandable sticky layer.

The thermal re-peelable layer 81 may be formed on the overall surface ofa principal plane, on the side on which the devices 3 are to be arrayed,of the base substrate 1, or selectively formed on the principal plane ofthe base substrate 1 at positions corresponding to those of the devices3. In the case of forming the thermal re-peelable layer 81 by coating,however, it is desirable to uniformly form the thermal re-peelable layer81 on the overall surface from the viewpoint of simplifying the process.

The base substrate 1 may be made from any material selected inconsideration of a combination with the devices 3; however, according tothis embodiment, the base substrate 1 is preferably made from a materialhaving a heat resistance allowing material to withstand even in thesubsequent heating step and a low expansion characteristic.

As the device 3, there can be used any type of device, examples of whichinclude a light emitting device, a liquid crystal control device, aphotoelectric transfer device, a piezoelectric device, a thin filmtransistor device, a thin film diode device, a resistance device, aswitching device, a micro-magnetic device, and a micro-optical device.

Here, it is not required for the sticky force of the thermal re-peelablelayer 81 to be perfectly eliminated by heating but it is sufficient forthe sticky force between the thermal re-peelable layer 81 and eachdevice 3 becomes smaller than the sticky force between a thermoplasticadhesive layer 82 (to be described later) and the device 3 at a specificheating temperature. To be more specific, if the sticky force betweenthe thermal re-peelable layer 81 and the device 3 becomes smaller thanthe sticky force between the thermoplastic adhesive layer 82 and thedevice 3, when a transfer substrate 82 is peeled from the base substrate1 as will be described later, the device 3 can be transferred from thebase substrate 1 to the transfer substrate 83.

To more certainly transfer the device 3, however, it may be desirable toset the combination of the thermal re-peelable layer 81 and thethermoplastic adhesive layer 82 so that the sticky force between thethermal re-peelable layer 81 and the device 3 becomes very smaller thanthe sticky force between the thermoplastic adhesive layer 82 and thedevice 3.

As shown in FIG. 18(a), the thermoplastic adhesive layer 82 is formed ona principal plane, taken as a transfer plane of the devices 3, on thetransfer substrate 83. The transfer substrate 83 is disposed in aspecific positional relationship with the base substrate 1 such that thedevices 3 are opposed to the thermoplastic adhesive layer 82.

The transfer substrate 82 may be made from any material selected inconsideration of a combination with the devices 3 and an application;however, according to this embodiment, the transfer substrate 83 ispreferably made from a material having a heat resistance allowingmaterial to withstand even in the subsequent heating step and a lowexpansion characteristic.

The thermoplastic adhesive layer 82 is made from a material capable ofgenerating an adhesive force by heating, thereby allowing the devices 3to be adhesively bonded to the transfer substrate 83 via thethermoplastic adhesive layer 82. Such a material is exemplified by athermoplastic resin or a solder. The thermoplastic adhesive layer 82 maybe formed overall on the transfer plane of the transfer substrate 83, orformed partially on the transfer plane at positions corresponding tothose of the devices 3.

To transfer the devices 3, as shown in FIG. 18(b), the transfersubstrate 83: is disposed in a specific positional relationship with thebase substrate 1 and is then brought into press-contact therewith, andin such a state, the thermal re-peelable layer 81 is heated by givingheat H to the overall surface by a heat source such as an oven, toreduce the sticky force of the thermal re-peelable layer 81 against thedevices 3, whereby the devices 3 become peelable from the thermalre-peelable layer 81. The thermoplastic adhesive layer 82 is softened byheating the layer 82, and is then cooled to be cured, to fix the devices3 to the thermoplastic adhesive layer 82. That is to say, the softenedthermoplastic adhesive layer 82 exhibits an adhesive force against thedevices 3. When the thermoplastic adhesive layer 82 is softened, theheating is stopped, to cool and cure the thermoplastic adhesive layer82, so that the devices 3 are transferred to the transfer substrate 83via the thermoplastic adhesive layer 82. The transfer substrate 83 isthen peeled from the base substrate 1, and the thermoplastic adhesivelayer 82 is cooled to room temperature, whereby the devices 3 arecertainly fixed to the transfer substrate 83. The transfer step is thusaccomplished.

FIG. 18(c) shows a state after the transfer substrate 83 is peeled fromthe base substrate 21, wherein the devices 3 are left as transferred onthe thermoplastic adhesive layer 82.

In this way, the devices 3 can be transferred from the base substrate 1to the transfer substrate 83.

In the device transferring method according to the third embodimentdescribed above, since the peeling of the devices 3 from the basesubstrate 1 and the adhesive bonding of the devices 3 to the transfersubstrate 83 can be performed only by the heating process, it ispossible to eliminate the need of providing an attracting head and anultraviolet irradiation apparatus, which has been required in the caseof using an ultraviolet reactive type material, and hence to transferthe devices 3 with a simple configuration. Since the transfer process issimple, the positioning of the devices 3 can be easily, certainlyperformed, so that it is possible to accurately transfer the deviceswithout occurrence of any positional deviation in transferred devices.Further, by positioning a reference one of the devices 3 to betransferred at a specific position, the other devices to be transferredare collectively positioned at specific positions, it is possible toaccurately transfer the devices without occurrence of any deviation inmounting position of each device.

According to this device transferring method pursuant to an embodimentof the present invention, since the peeling of the devices 3 from thebase substrate 1 and the adhesive bonding of the devices 3 to thetransfer substrate 83 are substantially, simultaneously performed, it ispossible to transfer the devices 3 for a short time, and hence tosignificantly shorten the mounting time of the devices 3.

According to this device transferring method pursuant to an embodimentof the present invention, since the devices 3 are fixed to the transfersubstrate 83 by using the thermoplastic adhesive layer 82, if thetransfer position of a device 3 is needed to be corrected or a device 3is peeled for some reason, it is possible to peel the device 3 byre-heating the thermoplastic adhesive layer 82.

If the thermoplastic adhesive layer 82 is made from a solder, thethermoplastic adhesive layer 82 is able to serve as wiring. In thiscase, it is possible to omit a wiring formation step and hence tosimplify a process of fabricating an electronic part or the like, and itis possible to simplify the configuration of an electronic parts or thelike and hence to reduce the cost of the electronic part.

According to this device transferring method pursuant to an embodimentof the present invention, the devices 3 are fixed to the base substrate1 by using the thermal re-peelable layer. If the devices 3 are fixed tothe base substrate 1 by using an ultraviolet-curing type resin, theultraviolet-curing resin is cured by heating to be adhesively bonded,thereby failing to transfer the devices 3 to the transfer substrate.Further, in this case, the transfer of the devices requires both aprocess of irradiating the ultraviolet-curing resin with ultravioletrays and a process of heating the thermoplastic adhesive layer 82, sothat the transfer work is complicated. On the contrary, according tothis transfer method, since the devices 3 are fixed to the basesubstrate 1 by using the thermal re-peelable layer, it is possible tosimply, certainly transfer the devices 3 from the base substrate 1 tothe transfer substrate.

In an embodiment, the heating of the thermal re-peelable layer 81 andthe thermoplastic adhesive layer 82 is performed by overall heatingusing a heat source such as an oven; however, the present invention isnot limited thereto. For example, as shown in FIG. 20, the thermalre-peelable layer 81 and the thermoplastic adhesive layer 82 can beheated by irradiating them with laser beams L from the back surface ofthe base substrate 1 and the back surface of the transfer substrate 6.To be more specific, the thermal re-peelable layer 81 is heated byirradiating the layer 81 with the laser beams L, to reduce the stickyforce of the layer 81 against the devices 3. As a result, the devices 3are peelable from the thermal re-peelable layer 81. Meanwhile, thethermoplastic adhesive layer 82 is heated by irradiating the layer 82with the laser beams L, to be softened, thereby exhibiting the adhesiveforce against the devices 3. Accordingly, by stopping, when thethermoplastic adhesive layer 82 is softened, the laser irradiation, tocool and cure the thermoplastic adhesive layer 82, the devices 3 arefixed to the transfer substrate 83 by means of the thermoplasticadhesive layer 82. In this way, the devices 3 can be transferred fromthe base substrate 1 to the transfer substrate 83. In this case, each ofthe base substrate 1 and the transfer substrate 6 preferably has a lighttransmissivity because it is required to perform laser irradiation fromthe back surface side of each of the base substrate 1 and the transfersubstrate 6 at the time of transfer of the devices 3.

In the example shown in FIG. 20, the overall surfaces of the basesubstrate 1 and the transfer substrate 6 are irradiated with the laserbeams L; however, as shown in FIG. 21, the portions corresponding to thedevices 3 may be selectively irradiated with the laser beams L. That isto say, only portions, corresponding to the devices 3 to be transferred,of each of the thermal re-peelable layer 81 and the thermoplasticadhesive layer 82 may be heated. Each of the thermal re-peelable layer81 and the thermoplastic adhesive layer 82 may be indirectly heated byheating the devices 3. When the devices 3 to be transferred are heatedby irradiating the devices 3 with the laser beams L, the heat istransferred to the thermal re-peelable layer 81 to heat the thermalre-peelable layer 81, to reduce the sticky force of the thermalre-peelable layer 81 against the devices 3, thereby making the devices 3peelable from the layer 81. The heat of the devices 3 is alsotransmitted to the thermoplastic adhesive layer 82, to soften the layer82, thereby exhibiting the adhesive force against the devices 3.Accordingly, by stopping, when the thermoplastic adhesive layer 82 issoftened, the laser irradiation, to cool and cure the layer 82, wherebythe devices 3 are fixed to the transfer substrate 83 by means of thethermoplastic adhesive layer 82. In this way, the devices 3 can betransferred from the base substrate 1 to the transfer substrate 83. Evenin this case, the same effect as that described above can be obtained.Also, in this case, the devices 3 may be irradiated with the laser beamsfrom the back surface side of either the base substrate 1 or thetransfer substrate 6.

In this case, as shown in FIG. 21, since only the devices 3 areselectively irradiated with the laser beams from the back surface sideof the transfer substrate 6, portions, other than the portions to whichthe devices 3 are to be fixed, of the thermoplastic adhesive layer 82are not fluidized by softening, so that the devices 3 can be moreaccurately transferred. Also, the use of the laser beams makes itpossible to heat very narrow portions of each of the thermal re-peelablelayer 81 and the thermoplastic adhesive layer 82 for a short time, andhence to shorten the mounting time of the devices 3. Since the heatedareas of each of the thermal re-peelable layer 81 and the thermoplasticadhesive layer 82 are small, such areas are not affected by the thermalcontraction characteristic of the base substrate 1, so that it ispossible to accurately transfer the devices 3.

Since the devices 3 can be selectively heated by laser irradiation, onlya desired one of the devices 3 formed in array on the base substrate 1can be selectively transferred, that is, the devices 3 can beselectively transferred. This makes it possible to efficiently mount thedevices.

Since the devices 3 can be selectively heated by laser irradiation, evenif the devices 3 are of different kinds, they can be simply transferredon the same substrate. As one example, there will be described a methodof transferring devices of one kind to a substrate, on which devices ofanother kind are previously mounted, by using laser irradiation.

As shown in FIG. 22(a), a thermoplastic adhesive layer 82 made from athermoplastic resin is formed on a transfer substrate 83 and devices 3of one kind are mounted on the thermoplastic adhesive layer 82 in such amanner as to be spaced at specific intervals. Meanwhile, a thermalre-peelable layer 81 is formed on a base substrate 81 and devices 7 ofanother kind are arrayed on the thermal re-peelable layer 81 in such amanner as to be spaced from each other at specific intervals. Here, theheight of the device 7 is set to be larger than that of the device 3.

To transfer the devices 7 of another kind, as shown in FIG. 22(b), thetransfer substrate 83 is disposed in a specific positional relationshipwith the base substrate 1 and is then brought into press-contacttherewith, and in such a state, only the devices 7 are selectivelyirradiated with laser beams L from the back surface side of the transfersubstrate 83, to be thus heated. The heat of the devices 7 istransmitted to the thermal re-peelable layer 81, to heat portions,corresponding to the devices 7, of the peelable layer 2, to reduce thesticky force of the thermal re-peelable layer 81 against the devices 7,thereby making the devices 7 peelable from the thermal re-peelable layer81. The heat of the devices 7 is also transmitted to the thermoplasticadhesive layer 82, to soften portions, corresponding to the devices 7,of the thermoplastic adhesive layer 82. As a result, the portions,corresponding to the devices 7, of the thermoplastic adhesive layer 82exhibit the adhesive forces against the devices 7. In this case, sincethe heated areas of the thermal re-peelable layer 81 are small, they arenot affected by the thermal contraction characteristic of the basesubstrate 1, whereby the devices can be accurately positioned. When thethermoplastic adhesive layer 82 is softened, the heating is stopped, tocool and cure the thermoplastic adhesive layer 82, so that the devices 7are fixed to the transfer substrate 83 via the thermoplastic adhesivelayer 82. In this way, the devices 7 can be transferred from the basesubstrate 1 to the transfer substrate 83. The transfer substrate 83 isthen peeled from the base substrate 1, and the thermoplastic adhesivelayer 82 is cooled to room temperature, whereby the devices 3 arecertainly fixed to the transfer substrate 83. The transfer step is thusaccomplished.

FIG. 22(c) shows a state after the transfer substrate 83 is peeled fromthe base substrate 1, wherein the devices 8 of another kind are left astransferred to the thermoplastic adhesive layer 82 in such a manner asto be located among the devices 3.

In this transfer, since the devices 3 previously mounted to the transfersubstrate 83 are not irradiated with the laser beams L, and therefore,not heated, portions, corresponding to the devices 3, of thethermoplastic adhesive layer 82 are not softened. Also, since the heatof the devices 7 is not transmitted to the portions, corresponding tothe devices 3 previously mounted adjacent to the devices 7, of thethermoplastic adhesive layer 82, the fixed states of the devices 3adjacent to the devices 7 are not thermally affected. As a result, atthe time of transfer of the devices 7 of another kind to the transfersubstrate 83, it is possible to prevent occurrence of peeling orpositional deviation of the devices 3 due to softening of the portions,corresponding to the devices 3, of the thermoplastic adhesive layer 82.In this way, the devices 7 of another kind can be accurately transferredto the transfer substrate 83, on which the devices 3 are previouslymounted, without occurrence of any positional deviation of the devices3.

Accordingly, a plurality of kinds of devices different in height can beaccurately transferred to one substrate by the above-described transfermethod. In this transfer method, however, as described above, theheights of devices to be transferred later are required to be largerthan those of devices previously mounted to a transfer substrate.

It is to be noted that the device used for the device transferringmethod of the present invention is not limited to that (device 3)described in this embodiment but may be configured as an electronic partin the form of a chip in which a device is buried in an insulator suchas a plastic material. Even in this case, the same effect as thatdescribed above can be obtained.

It is very useful to apply the above-described transfer method totransfer of devices in fabrication of an active matrix type imagedisplay unit.

In an active matrix type image display unit, light emitting devices ofR, G, and B must be disposed adjacent to an Si transistor as a drivedevice by sequentially transferring the light emitting devices of R, G,and B to positions close to the Si transistor. In this transfer,however, since the Si transistor has a very high thermal conductivity,if heat is applied thereto, an inner circuit thereof may be broken. Suchan inconvenience can be solved by the above-described transfer methodusing laser irradiation. That is to say, according to this transfermethod, the transfer of heat to the Si transistor can be avoided duringthe step of transferring the light emitting devices of R, G, and B.

As an application example of the above-described transfer methodaccording to an embodiment of the present invention, a device arrayingmethod and an image display unit fabricating method using the two-stepenlarged transfer method will be described below.

In an embodiment, in the concrete method of arraying light emittingdevices shown in FIGS. 10 to 16, a light absorbing material forincreasing a light absorptivity against laser beams is contained in eachof the adhesive layers 45 and 56.

In the device arraying method and image display unit fabricating methodaccording to an embodiment, light emitting diodes 42 are transferred toa second substrate 60 by making use of the above transfer method. Asshown in FIG. 22, a thermal re-peelable layer 85 is previously formed ona principal plane of a third temporarily holding member 84 made from amaterial having a light transmissivity. A second temporarily holdingmember 47 is brought into press-contact with the third temporarilyholding member 84 such that the thermal re-peelable layer 85 is opposedto the upper surface, on the side provided with an anode side electrode49, of each light emitting diode 42 to be transferred. In such a state,a portion, corresponding to the light emitting diode 42, of a peelablelayer 48 is irradiated with laser beams from the back surface side ofthe second temporarily holding member 47. Accordingly, if the peelablelayer 48 is made from polyimide, peeling occurs by abrasion of polyimideat the interface between polyimide and a quartz substrate, with a resultthat the light emitting diode 42 is transferred to the thermalre-peelable layer 85 of the third temporarily holding member 84.

As shown in FIG. 23, a thermoplastic adhesive layer 86 is previouslyformed on the second substrate 60. The second substrate 60 is disposedin a specific positional relationship with the third temporarily holdingmember 84 such that the light emitting diodes 42 are opposed to thethermoplastic adhesive layer 86. Subsequently, as shown in FIG. 24, onlya portion, corresponding to the resin-covered chip (light emitting diode42 covered with an adhesive layer 45) to be transferred, of the thermalre-peelable layer 85 is irradiated with laser beams 56 from the backsurface side of the third temporarily holding member 84 to be thusheated, and simultaneously only a portion, corresponding theresin-covered chip, of the thermoplastic adhesive layer 86 is irradiatedwith the laser beams 56 from the back surface side of the secondsubstrate 60 to be thus heated. As a result, the sticky force of theportion, corresponding to the resin-covered chip, of the thermalre-peelable layer 85 against the resin-covered chip is reduced, wherebythe resin-covered chip becomes peelable from the thermal re-peelablelayer 85. The portion, corresponding to the resin-covered chip, of thethermoplastic adhesive layer 86 is softened by laser irradiation. Thesoftened portion of the thermoplastic adhesive layer 86 is then cooledto be cured, whereby the resin-covered chip is fixed to the secondsubstrate 60.

An electrode layer 57 serving as a shadow mask may be disposed on thesecond substrate 60. In this case, by irradiating a portion,corresponding to the target portion of the thermoplastic adhesive layer86, of the electrode layer 57 with the laser beams 56 so as to heat theportion of the electrode layer 57, the target portion of thethermoplastic adhesive layer 86 can be indirectly heated. In particular,as shown in FIG. 25, a black chromium layer 58 may be formed on asurface, on the screen side, that is, on the viewer side, of theelectrode layer 57. With this provision of the black chromium layer 58,it is possible to improve the contrast of an image, and also to increasean energy absorptivity of the electrode layer 57 via the black chromiumlayer 58 and hence to efficiently heat the target portion of thethermoplastic adhesive layer 86 by selectively irradiated laser beams56. After that, the same steps as those described above is repeated, tofabricate a drive panel.

According to the above-described method of arraying light emittingdevices, in the transfer (second transferring step) of the resin-coveredchip to the second substrate, the thermal re-peelable layer 85 and thethermoplastic adhesive layer 86 are selectively heated by laserirradiation, to be thus cured, so that only the resin-covered chip to betransferred can be certainly transferred to the second substrate withoutexerting adverse effect on the adhesive bonded states of other parts.

INDUSTRIAL APPLICABILITY

According to a device transferring method pursuant to an embodiment ofthe present invention, only devices to be transferred can be quicklyshifted and with certainty and selectively transferred by selectivecuring of an adhesive resin due to selection laser irradiation. In thecase of overall heating, there are problems associated with largevariations in temperature condition of a furnace and positionalcondition. On the contrary, laser heating can ensure a stable heatingcondition, to realize stable adhesive bonding of the devices. Since anadhesive resin is not required to be selectively applied but may beoverall applied, it is possible to simplify the process. Also, sinceother parts are not affected by selective heating of the devices to betransferred due to selective laser irradiation, the devices can betransferred without peeling and positional deviation of the other parts.

According to a device arraying method pursuant to an embodiment of thepresent invention, since the devices can be efficiently and withcertainty transferred by using the above-described device transferringmethod, it is possible to readily perform enlarged transfer by means ofwhich the devices are transferred in such a manner as to be spaced fromeach other with an enlarged pitch.

According to an image display unit fabricating method pursuant to anembodiment of the present invention, it is possible to efficientlyre-array the light emitting devices, which have been formed on the firstsubstrate densely, that is, with a high degree of integration, on thesecond substrate in such a manner as to be spaced from each other withan enlarged pitch by using the above-described device transferringmethod, and hence to fabricate a precise image display unit with a highproductivity.

According to a device transferring method pursuant to an embodiment ofthe present invention, portions, corresponding to desired devices, ofthe adhesive layer can be selectively heated, by laser irradiation fromthe back surface side of the substrate, directly or indirectly via thedevices or wiring without heating portions, near devices other than thedevices to be transferred, of the adhesive layer. As a result, since thelight absorbing material for increasing the light absorptivity of theadhesive layer against laser beams is contained in the adhesive layer ordisposed in the vicinity of the adhesive layer, portions, correspondingto devices to be transferred, of the adhesive layer are allowed to moredesirably absorb the laser beams, and hence to be more desirably heated.As a result, it is possible to efficiently, selectively heat theportions, corresponding to the devices to be transferred, of theadhesive layer.

Since the laser beams are absorbed by the light absorbing materialhaving the light absorptivity against the laser beams, the laser beamsdo not reach the devices to be transferred, so that it is possible toprevent the devices to be transferred from being damaged by the laserbeams. As a result, it is possible to select any kind and wavelength ofthe laser beam irrespective of the material of the device, that is, withthe damage of the device by the laser beam not taken into account.

By selecting a material having a known laser beam absorptioncharacteristic as the light absorbing material, it is possible toestimate the heat generation amount of the light absorbing material uponheating, and hence to select a material being independent of the laserbeam absorption characteristic as the material of the device.

Since the material of the device is not dependent on the laser beam, itis possible to eliminate the work of selecting the material of the laserbeam and hence to simply select the material of the device. Also, sincethe light absorptivity of the adhesive layer against laser beams can beincreased by containing the light absorbing material in the adhesivematerial or disposing the light absorbing material in the vicinity ofthe adhesive layer and forming the adhesive layer over the entiresurface, it is possible to simplify the process.

Since portions, corresponding to devices to be transferred, of theadhesive layer can be efficiently heated by the presence of the lightabsorbing material, the time required to irradiate the devices with thelaser beams becomes short, and accordingly portions, near the devices tobe transferred, of the adhesive layer are not heated. As a result, thedesired devices can be transferred without exerting any effect on thefixed states of devices other than the devices to be transferred, thatis, without peeling and positional deviation of the other devices.

According to a device arraying method pursuant to an embodiment of thepresent invention, since desired devices are transferred by using theabove-described transferring method, the desired devices can beefficiently, certainly transferred without being damaged by laser beams.As a result, it is possible to smoothly perform enlarged transfer bymeans of which the desired devices are transferred in such a manner asto be spaced from each other with an enlarged pitch.

According to an image display unit fabricating method pursuant to anembodiment of the present invention, it is possible to efficientlyre-array the light emitting devices, which have been formed on the firstsubstrate densely, that is, with a high degree of integration, on thesecond substrate in such a manner as to be spaced from each other withan enlarged pitch by using the above-described device transferringmethod, and hence to fabricate a precise image display unit with a highproductivity.

A device transferring method according to an embodiment of the presentinvention includes:

-   -   a superimposing step of superimposing a second substrate having        a thermoplastic adhesive layer on a first substrate on which        devices are previously fixed in array via a thermal re-peelable        layer; and    -   a heating/cooling step of heating and cooling, in a state that        the devices are in contact with the thermoplastic adhesive        layer, the thermal re-peelable layer and the thermoplastic        adhesive layer, to make the devices peelable from the thermal        re-peelable layer and simultaneously melt and cure the        thermoplastic adhesive layer, thereby transferring the devices        to the second substrate.

With a device transferring method according to an embodiment of thepresent invention, since the peeling of the devices from the firstsubstrate and the adhesive bonding of the devices on the secondsubstrate can be performed only by the heating process, the devices canbe very simply transferred without the need of provision of members suchas an attracting head and an ultraviolet irradiation apparatus requiredin the case of using an ultraviolet-curing type material. Since thetransfer process is simple, it is possible to easily, certainly performthe positioning of the devices, and hence to accurately transfer thedevices without occurrence of any positional deviation of thetransferred devices.

In a device transferring method according to an embodiment of thepresent invention, since the peeling of the devices from the firstsubstrate and the adhesive bonding of the devices to the secondsubstrate can be substantially simultaneously performed only by theheating process, it is possible to realize the transfer for a shorttime, and hence to efficiently transfer the devices.

A device arraying method of re-arraying a plurality of devices arrayedon a first substrate to a second substrate according to an embodiment ofthe present invention includes:

-   -   a first transferring step of transferring the devices from the        first substrate to a temporarily holding member in such a manner        that the devices are spaced from each other with a pitch larger        than a pitch of the devices arrayed on the first substrate and        holding the devices on the temporarily holding member;    -   a covering step of covering the devices held on the temporarily        holding member with a resin;    -   a dicing step of dicing the resin so as to isolate the devices        from each other;    -   a second transferring step of transferring the resin-covered        devices held on the temporarily holding member to the second        substrate in such a manner that the resin-covered devices are        spaced from each other with a pitch larger than a pitch of the        resin-covered devices held on the temporarily holding member;    -   wherein the second transferring step includes:    -   a fixing step of fixing the resin-covered devices on a second        temporarily holding member via a thermal re-peelable layer;    -   a superimposing step of superimposing the second substrate        having a thermoplastic adhesive layer on the second temporarily        holding member; and    -   a heating/cooling step of heating and cooling, in a state that        the resin-covered devices are in contact with the thermoplastic        adhesive layer, the thermal re-peelable layer and the        thermoplastic adhesive layer, to make the resin-covered devices        peelable from the thermal re-peelable layer and simultaneously        melt and cure the thermoplastic adhesive layer, thereby        transferring the resin-covered devices to the second substrate.

With a device arraying method according to an embodiment of the presentinvention, since the devices can be efficiently, certainly performed byusing the above-described device transferring method, it is possible tosmoothly perform enlarged transfer by means of which the desired devicesare transferred in such a manner as to be spaced from each other with anenlarged pitch.

An image display unit fabricating method of fabricating an image displayunit including light emitting devices disposed in a matrix according toan embodiment of the present invention includes:

-   -   a first transferring step of transferring the light emitting        devices from the first substrate to a temporarily holding member        in such a manner that the light emitting devices are spaced from        each other with a pitch larger than a pitch of the light        emitting devices arrayed on the first substrate and holding the        light emitting devices on the temporarily holding member;    -   a covering step of covering the light emitting devices held on        the temporarily holding member with a resin;    -   a dicing step of dicing the resin so as to isolate the light        emitting devices from each other;    -   a second transferring step of transferring the resin-covered        devices held on the temporarily holding member to the second        substrate in such a manner that the resin-covered devices are        spaced from each other with a pitch larger than a pitch of the        resin-covered devices held on the temporarily holding member;    -   wherein the second transferring step includes:    -   a fixing step of fixing the resin-covered devices on a second        temporarily holding member via a thermal re-peelable layer;    -   a superimposing step of superimposing the second substrate        having a thermoplastic adhesive layer on the second temporarily        holding member; and    -   a heating/cooling step of heating and cooling, in a state that        the resin-covered devices are in contact with the thermoplastic        adhesive layer, the thermal re-peelable layer and the        thermoplastic adhesive layer, to make the resin-covered devices        peelable from the thermal re-peelable layer and simultaneously        melt and cure the thermoplastic adhesive layer, thereby        transferring the resin-covered devices to the second substrate.

With an image display unit fabricating method according to an embodimentof the present invention, it is possible to efficiently re-array thelight emitting devices, which have been formed on the first substratedensely, that is, with a high degree of integration, on the secondsubstrate in such a manner as to be spaced from each other with anenlarged pitch by using above-described device transferring method anddevice arraying method, and hence to fabricate a precise image displayunit with a high productivity.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present inventionwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A device transferring method of selectively transferring devicesarrayed on a first substrate to a second substrate on which an adhesiveresin layer is previously formed, the method comprising the steps of:selectively heating te adhesive resin layer on the second substrate bylaser irradiation from a back surface side of the second substrate; andcuring a selectively heated portion of the adhesive resin layer, therebyadhesively bonding devices to be transferred of the devices arrayed onthe first substrate to the second substrate.
 2. The transferring methodaccording to claim 1, wherein the heating step includes a step ofheating portions of said adhesive resin layer located at positionscorresponding to the devices to be transferred, by irradiating theportions of the adhesive resin layer with one or more laser beams. 3.The device transferring method according to claim 1, wherein the heatingstep includes a step of irradiating the devices to be transferred withlaser beams to heat the devices to be transferred thereby heatingportions of said adhesive resin layer located at positions correspondingto the devices to be transferred of the devices arrayed on the firstsubstrate.
 4. The device transferring method according to claim 1,wherein the heating step includes a step of irradiating one or morewiring portions, previously formed on the second substrate, with laserbeams to heat said wiring portions, thereby heating portions of theadhesive resin layer located on said wiring portions.
 5. The devicetransferring method according to claim 1, wherein the adhesive resinlayer includes a thermoplastic adhesive resin.
 6. The devicetransferring method according to claim 1, wherein the adhesive resinlayer includes thermosetting adhesive resin.
 7. The device transferringmethod according to claim 1, wherein the device is buried in aninsulating material.
 8. A device arraying method of re-arraying aplurality of devices arrayed on a first substrate to a second substrate,the method comprising the steps of: a first transferring step includingtransferring the devices from the first substrate to a temporarilyholding member such that the devices are spaced from each other with apitch larger than a pitch of the devices arrayed on the first substrateand holding the devices on the temporarily holding member; a coveringstep including covering the devices held on the temporarily holdingmember with a resin; a dicing step including dicing the resin so as toisolate the devices from each other; a second transferring stepincluding transferring the resin-covered devices held on the temporarilyholding member to the second substrate such that the resin-covereddevices are spaced from each other with a pitch larger than a pitch ofthe resin-covered devices held on the temporarily holding member;wherein the second transferring step includes the steps of selectivelyheating an adhesive resin layer on the second substrate by laserirradiation from a back surface side of the second substrate, and curingthe selectively heated portions of the adhesive resin layer, therebyadhesively bonding the devices to be transferred of the resin-covereddevices to the second substrate.
 9. A device arraying method accordingto claim 8, wherein the array pitch of the devices transferred to thetemporarily holding member in the first transferring step isapproximately an integer times the array pitch of the devices formed onthe first substrate, and the array pitch of the devices transferred tothe second transfer substrate in the second transferring step isapproximately integer times the array pitch of the devices transferredto the temporarily holding member in the first transferring step. 10.The device arraying method according to claim 8, wherein the device is asemiconductor device using a nitride semiconductor.
 11. The devicearraying method according to claim 8, wherein the device is selectedfrom the group consisting of a light emitting device, a liquid crystalcontrol device, a photoelectric transfer device, a piezoelectric device,a thin film transistor device, a thin film diode device, a resistancedevice, a switching device, a micro-magnetic device, and a micro-opticaldevice, and parts of the selected device thereof.
 12. An image displayunit fabricating method of fabricating an image display unit includinglight emitting devices disposed in a matrix, the method comprising thesteps of: a first transferring step including transferring the lightemitting devices from the first substrate to a temporarily holdingmember such that the light emitting devices are spaced from each otherwith a pitch larger than a pitch of the light emitting devices arrayedon the first substrate and holding the light emitting devices on thetemporarily holding member, a covering step including covering the lightemitting devices held on the temporarily holding member with a resin; adicing step including dicing the resin so as to isolate the lightemitting devices from each other, a second transferring step includingtransferring the resin-covered light emitting devices held on thetemporarily holding member to the second substrate such that theresin-covered light emitting devices are spaced from each other with apitch larger than a pitch of the resin covered light emitting devicesheld on the temporarily holding member; wherein the second transferringstep includes the steps of selectively heating an adhesive resin layerpreviously applied on a first surface side of the second substrate bylaser irradiation from a second surface side of the second substrate,and curing the selectively heated portions of the adhesive resin layer,thereby adhesively bonding the devices to be transferred of theresin-covered light emitting devices to the second substrate.